You're right, however, my Priest had no spells in the Air realm yet. I figure that Cure Poison would help with the Whirlwind spell that he is about to receive, in terms of SPs (and it's handy to dump all those Cure Poison potions at Burz).
Edit: Curing Poison before it runs its course may increase the Priest's Divinity/Air Magic skill, instead of using a potion which increases nothing. It's a long way to Arnika at this point, and any skill increases are welcome.

Level 8:
Priest: Whirlwind
Alchemist: Fire Bomb
Psionic: Ego Whip
Mage: X-Ray
A hard fought level up. Many Metallic Slimes are starting to show up (they have damage resistance, not sure how much). Magic is almost necessary against them, they also have pretty high HPs.
The completionist in me likes to fight every set battle, open every treasure chest, and detect and grab every item available. I swam the waterfall and used Detect Secrets to grab the two items hidden on the shelf. I then sold all unneeded items to Burz, and restocked on ammo.
Speaking of which, slimes can be your best friend so early on. They give decent experience, skill ups, gold, and can drop decent items (nothing special yet).
I sometimes get criticism, but with most parties, the best path is to keep to level 5 or 6 before leaving the Monastery, and save level ups until just before Arnika, where you take your level ups. With most parties, this is a valid strategy, as hybrids and non magic users are item-dependent.
This is not the case with a MDP. The five primary magic casters (Bishop, Priest, Alchemist, Psionic, and Mage), are not very equipment-dependent (especially the robe classes, the Psionic and Mage). The primary focus of a MDP is to deliver magic damage, and levelling up is the best way to reach that goal (more SPs and more powerful magic). Therefore, I have chosen to camp the Monastery until I feel that the Arnika Road will be comfortable (thankfully, Burz can restock ammo, as well as buy unnecessary items, not to mention you can mix potions and sell for a profit and Alchemy skill ups.) I have no way to replenish SPs besides resting, so this seems like a valid strategy.
I have completely cleared the Lower Monastery, except for the Wheel Key/Cierdan's Tomb side quest. I am about to visit the Upper Monastery, where there are a good amount of rats, even a few set Rabid Rats (there is no avoiding this, so you might as well be higher level when fighting them). Also, there are set Higardi thieves that can drop good Bard equipment (Mercucio's Blade, Prospero's Cloak, Ariel's Slippers). I will farm them, this might take a while.
The Priest finally has a decent AOE attack spell, the Alchemist finally has a good Fire spell from long range, the Psionic can mentally lash enemies that get too close, and the Mage can see where enemies are all over the map. This level up is a real game-changer (normally, you don't get level 4 spellbooks until Crock). Also, the Gadgeteer crafted for herself a Doubleshot Crossbow (2 shots per attack is unheard of so early in the game).

Level 9:
Priest: Magic Screen
Alchemist: Acid Bomb
Psionic: Armormelt
Mage: Enchanted Blade
This was another very hard level up. Level ups increase exponentially (the experience requirement doubles every level, until a certain point). I completely cleaned out the Upper Monastery. I managed to get the 3 Bard specialty items (Mercucio's Blade, Prospero's Cloak, and Ariel's Slippers) with much difficulty (don't ask how many retries/how long it took).
Level 10 Emerald Slimes are making an appearance. They give good experience but take a long time to kill.
The Bard got an Angel's Tongue (Bless) instrument. The Gadgeteer got a Lightning Rod (Energy Blast) gadget. The Priest got the Bless spellbook and the Psionic got the Divine Trap spellbook in the Upper Monastery library.
Edit: Magic Screen apparently is sorely needed. In the last fight with a level 10 Emerald Slime (while my party was still at level 8), my Alchemist got Nauseated, and my Priest got both Paralyzed and Nauseated with one hit. It could be the 2 level deficit combined with the lack of magic protection (Magic Screen, Soul/Element Shield).
Thankfully, nothing was permanent (no Death, Disease, Draining occured). Those are the worst conditions.

Level 10:
Priest: Cure Lesser Condition
Alchemist: Element Shield
Psionic: Haste
Mage: Whipping Rocks
Level 10 was another tough one. I fought off 2 Greater Seekers (level 12) while I was level 9, barely surviving. The Mage has finally learned an Earth realm skill, and I've been avoiding the Vampire Bats until I'm tough enough.
Edit: I got a Vampire Bat Wing, after fighting with 4 of them. It took some farming.

Level 11:
Priest: Heal All
Alchemist: Toxic Cloud
Psionic: Instant Death
Mage: Crush
This is the last time the experience requirement to gain the next level up doubles. It literally takes the same amount of experience to go from level 1 to level 10, as it does from level 10 to level 11, due to exponential growth. From now on the factor will be 1.6 instead of 2.
My Bard and Gadgeteer have 2 attacks per round now, due to a combination of high Ranged Combat and Bow skills, plus very high Dexterity, which they will max next level up. I have found them to be competent at both melee and ranged combat, which is why I am stressing Strength and Dexterity first, then I will focus on Speed and Senses for higher initiative and more attacks per round. Intelligence and Piety are near useless for a non-caster, and Vitality is an ok stat.
For my casters, all realms have been opened up and trained as much as possible without cheating or excessive grinding. That is six realms each for the Mage and Psionic, five realms for the Alchemist (no Mental realm for him), and five realms for the Priest (he has a very weak Mental realm, so I'm skipping it until Arnika, where I can give him a book of Identify Item. I could train my Priest to be the ID item guy, since the Psionic won't want to waste spell points in his most important realm, Mental.) They are getting Intelligence to 95 before the +5 Trynton fountain, and are maxing Speed for Snakespeed. Next is Senses and Piety for more initiative, spell points and stamina. Strength and Dexterity are stats more suited to physical combat, which is why they are last priority, and again, Vitality is an ok stat (none of the casters will have very high hit points anyways, and they have the worst tier fighting abilities.)
I have a self-imposed rule about not using spells unless necessary. No opening the casket repeatedly in the Lower Monastery to cast Cure Lesser Condition and Heal Wounds to train. No resting to recast buffs/regain spell points until at least 1 battle has been fought. No repeatedly examining trapped chests.
Both the Lower and Upper Monastery have been completely cleaned out (every set battle fought, every chest opened, every item grabbed, both hidden and obvious. The Wheel Key/Cierdan's Tomb side quest remains of course, so I will set a portal right in front of the door, and portal in and out once I reach Arnika.
I am getting a lot of easy Metallic Slimes to fight, plus the occasional Pestilent Rats, Vampire Bats, and Emerald Slimes. Rarely will level 12 Greater Seekers spawn, I'm almost at their level. I really have to watch out for level 14 Flesheater Smiles, they are nasty if you are low level. They start out neutral fortunately, so you can usually get away from them. As far as I've seen, they are the highest level monster that can spawn in the Monastery.
I still find myself having to rest to regain spell points after one good battle, or 2 or 3 easy ones. That's the thing about a MDP, they are so reliant on magic, that I can't go too far without resting. I still make sure to train everyone in at least one physical skill for the times when I'm out of magic.

Correction: The factor is only 1.2. (It is because the factor is this low that Bishops end up about 3 levels behind Fighters at higher levels, assuming that level ups are taken as they come and there's no deeping XP gap between characters (a constant gap is fine).)

First, we should include the next line of the table:
Level 13: 1,187,840

1187840 / 819200 = 1.45 (note that this is not 1.6)

That table seems to indicate the *total* amount of XP needed to level up, so let's look at the *differences*, that is, the amount of XP needed to go from one level to the next. We have the following here:
Level 10->11: 256,000
Level 11->12: 307,200
Level 12->13: 368,640

307200 / 256000 = 1.2
368640 / 307200 = 1.2

So, the amount of additional XP needed to gain one level, once you're past level 10, increases by a factor of 1.2 each level. This pattern continues until integer overflow occurs, which appears to happen at level 50 for the slow leveling classes, and later for the fast leveling ones. (From what I understand, you can level past 50, but the level in your status screen won't change.)

I see. I guess we were just looking at the table in two different ways. Thankfully, the exponential growth slows down, only requiring 1.2X the experience to get to the next level as it did for the previous level. This would explain why level ups can skyrocket in Arnika, because as you level up, you will get more powerful enemies, which give better experience, which makes up for that 1.2 factor. I believe that the toughest monsters you can grind there are level 22 Savant Minion. While doing so is considered tedious by most players, it makes the rest of the game a cakewalk, having all the good spells and an actual way to replace magic points. It's also surprisingly fun (and tedious sometimes) to watch your attributes/skills skyrocket as you get more powerful.
There is no logical reason I can think of that Burz doesn't sell Magic Nectar potions, it kind of gives MDPs an unfair disadvantage. I think the problem is how I am viewing the game. W8 almost requires that parties have physical damage capability, which is why MPNorman makes his Priest/Alchemist combat ready, putting points into Strength and Dexterity.
I have a different view on those two classes, going the route of the Psionic/Mage (Intelligence and Speed, then Senses and Piety). This gives a quadruple magic blast on the enemies every round very quickly (X6 a round once the Bard and Gadgeteer actually get good instruments and gadgets). Of course, this comes at the cost of having 2 decent fighters with melee and range, and 4 weak fighters.
This is why I'm going the route of all humans, getting decent numbers (45+) in all stats allows you to max out whatever you want, up to 4 stats, by level 30, certainly before the end of the game if you don't mind grinding the enemies in the Mountain Wilderness, which aren't nearly as threatening as the ones on AP. Not to mention, I picked the easiest two experience tracks to level up for my MDP (specialists and specialist casters).
Gender is really a non-issue. I did make my Bard and Gadgeteer female for the early stamina regeneration items, and I made my casters male for variety except the Mage, who is female. Really, much better items can be found later.
In my opinion, the *best for me* setup would be to have the Bard and Gadgeteer do Swords and Shields, with Bows and Crossbows for range, and Music/Engineering for "magic". The Priest is the only one with the Mace&Flail skill, so he does that with a Shield, with Slings for range.
The other 3 have very limited weapon choices, Daggers and Wands and Short Staves would require them to melee enemies (and none of these justify going into melee range IMO). Of these 3, the Alchemist is physically the toughest, with better HPs and armor choices, so he gets the Staff of Doom (training with a Quarterstaff). He is throwing darts and slinging stones when he can, but the SOD is cursed, so later on he won't be able to use ranged attacks (at least he gets good Alchemy spells). Also, he may be tough enough to hold a flank with the SOD, or I could leave him in the center and attack from extended range.
This leaves the two weaklings, the Psionic and Mage. No Dual Weapons, no Shield, nothing in the off hand. Since the Alchemist already has dibs on the SOD, there is no reason to melee. They are going Ranged Combat/Throwing&Sling all the way, hoping for a KO% with stones.

Level 12:
Priest: Cure Paralysis
Alchemist: Cure Poison
Psionic: Psionic Blast
Mage: Noxious Fumes
Both the Bard and Gadgeteer have maxed Dexterity for Reflextion expert skill. The party is at the same level to face level 12 Greater Seekers, if they do spawn. Level 14 Flesheater Slimes are still a worry, as I will be avoiding them until the party is ready.
Edit: I got lucky and faced 2 level 12 Greater Seekers in the Upper Monastery garden, and I was able to take them down without a problem. However, due to my high level, I also often face much lower enemies, even level 1 Bats. There seems to be a wild swing once you get to a high level, between easy, hard, and everything in between.

Level 13:
Priest: Instant Death
Alchemist: Crush
Psionic: Set Portal/Return to Portal
Mage: Iceball
This was a difficult level, taking a week to complete. This was largely due to lower level spawns, from level 1 up to level 12 Greater Seekers (I got lucky a few times). The reliable enemies were Metallic Slimes and Emerald Slimes, followed up by Spewing Slimes.
The theme here is that slimes can be good. They generate experience, skill-ups, gold, and item drops. The last one is why I have decent equipment, for the Monastery.

Level 14:
Priest: Lightning
Alchemist: Draining Cloud
Psionic: Slow
Mage: Freeze All
I just got access to level 6 spells. which are game-changing (Priest Fire Magic, and Alchemist Divine Magic). There is a lot of room for skill improvements, which is why I grind the Lower and Upper Monastery. The Arnika Road challenge lies ahead of me, so I want to be ready.

Why Lightning over Resurrection?

At your level, Lightning has a chance to fizzle at any power level greater than 1 (I believe it's 6% per power past 1, in addition to what you get for having low Fire Magic skill), while Resurrection is fully useful at this point.

Also, why Draining Cloud, which is pretty much useless (might have some *minor* use if the enemies are using Element Shield), rather than Quicksand which is great for killing lower level enemies (some of which have high HP)?

Also, why Slow for the Psionic? Slow is a horrible spell; if you get it to work, it will slow down the enemy's animations, causing the game's already long battles to drag out even further. Also, it seems rather silly to pick up a 2nd level spell when you can pick up to a 6th level spell.

Lightning, at least to me, is fairly obvious. The Priest only gets 2 fire realm skills, Light (level 1, I gave him the free spellbook to train fire magic), and Lightning (level 14). That is a huge gap, leaving many levels to train his fire magic skill. However, since the only non-cheesy way to train it is to cast Light every 24 hours, it skills up slowly (my fire magic skill is only in the 20s). Giving him Lightning will allow him to cast it at PL1, finally giving him a fire attack spell to train with. The result will be underwhelming for the first few levels, as will most spells when you first get them. It's not a big deal, as I am facing a lot of low level spawns, the goal isn't high damage anymore, it's training the realms.
At this point, the chance of death is pretty low, so Resurrection is pointless. I believe the highest level enemies that can spawn on Arnika Road are level 10 Higardi Brigand. Due to my high level, I will be seeing a lot of them. They are annoyingly fast for their level, and almost always go first, which is why status debuffs are important, as well as high magic damage. Each caster should be able to chop 20-30% of an enemy's HPs off, so working in tandem is the way of the MDP, rather than quick kills. This will require a lot of SPs, hence the heavy training. Even my weakling Psionic and Mage are getting 2 swings and 2 attacks per round with slings, due to very high Speed, as I know that some physical damage is essential. As for the Monastery, at level 14, everything except neutral (at first) Flesheater Slimes is below my level, and I don't feel threatened anymore. I'm actually avoiding them, as they get many attacks, and can disease and drain party members. Fortunately, the yellow dots on the X-Ray map give them away, making them easy to avoid.
Similarly, the Alchemist gets very few divine realm skills. Heal Wounds (level 1) is good for the early game, so it can be trained early on when I'm weak enough to actually take damage. I don't get hit very often anymore, due to high level, high AC and buffs, so there are very few opportunities to train his divine realm skill (it's only in the teens). The other spell, Summon Elemental (level 11), I don't have much use for. I like to use my Bard and Gadgeteer as archers, once they've cast Bless and Energy Blast in the first round to train Music and Engineering slowly. An elemental will often get in the way, and if you hit it accidentally, they can turn hostile on you (and they are often low level when you do summon them, not very helpful). This would make Draining Cloud his only divine realm attack spell (just like the Priest, he has no use for Resurrection at this time). Perhaps I will pick Quicksand at the next level up, when it can be cast at PL2 safely (my playstyle with an MDP isn't quick kills).
Again, this comes down to lack of decent spells in a realm. The Psionic only had Paralyze as a water realm spell, which had to compete with the Mage's Freeze Flesh and Freeze All spells. Paralyze is only thrown range, while Slow has long range and works on the whole enemy group. If it doesn't work, who cares? The skill up only cares if you attempt to use the spell. It it works, it actually can be useful if a group of level 21 Savant Slashers are attempting to surround your party (it seems to reduce the distance an enemy moves when it closes with you, buying you more time, as well as reducing their chance to hit and defend). I only use it when I feel that his water realm skill is lagging behind. The Psionic is extremely lopsided with his decent spells in each realm, making the water and earth realm skills more annoying to level up (Cure Lesser Condition and Armormelt aren't terrible spells to have). There has to be a way to keep them near the realm skill of the others.

Level 15:
Priest: Lifesteal
Alchemist: Boiling Blood
Psionic: Might to Magic
Mage: Firestorm
The party is looking good, about to get expert skills at level 16 (Powerstrike for the Bard, Snake Speed for the casters). The Gadgeteer, due to her higher profession requirements, will have to wait until level 17 for Powerstrike.
Edit: There are not too many good level 6 spells, at least for an MDP. I have imposed on myself to actually take every spell pick as I get them. I sometimes pick spells just to give extra spell points in each realm, even if I will never actually use them.