Here are some interesting character setups to consider:

Early game:

Dragonewt Fighter: Fighters get high HP. Dragonewts get a breath attack that depends on current HP. This gives you a very powerful breath attack early in the game that, at level 8, hits the entire front row of enemies. For even more damage, try the EX skill Cruelty for a further 25% bonus. (At high levels, once the breath damage limit is easily reached, Mark of Ruin is good because it provides a bigger bonus.) There is no reason not to use this breath attack every battle, especially since it will be more powerful than their regular attack. This character should be male because the game is sexist and doesn't let women wield the Golden Axe. I have used this setup, but without Cruelty because I needed someone for Mysterious Bag.

Faerie Brawler: This setup looks like it could work rather well. Strength and Vitality cap too low to get bonuses, but you get 5 AC in addition to the Lower AC ability. The faerie's equipment limitations aren't a big deal because most of them are "Lowered AC Ability" OFF, making them less useful anyway. Faeries can use the Brass Knuckle, and then there is the Star Rod (obtained from an event in Hostrana) which does 4-22 damage (a lot for that part of the game), is Lower AC ON, and is only usable by faeries. Later on, Faeries can use the Death Arm (remember to remove the curse!), and there's the hidden spot where you can turn this character into a Devilish (though I recommend Spirit Pact instead). I haven't tried this setup, and I'm already past the point where it would be useful, but it looks like this setup would actually work surprisingly well. I recommend raising the damage of the Brass Knuckles with alchemy to compensate for low strength.

Bard with Magic Essence: Magic Essence works with items that cast mage spells, like the harp that causes sleep. Good early game setup for causing status ailments.

Late game:
Don Mags (Spirit Pact): Look at those bonuses! 300% fire and ice! Even better, this monster becomes a mage and can get even bigger bonuses at higher levels. Try for Spirit Contract (for even more damage) or Magic Essence (for reliability and status inflection).

Faerie Bishop: High Agility, better AC than a bishop of another race would likely get, and access (eventually) to powerful spells. I recommend Magic Essence for status ailments, though if that's already covered, Hand of Kindness can be useful at higher levels. I'm using one, and I really like her.

Dragonewt Ninja with Death Breath: This setup is only possible in the post-game (either Spirit Pact a monster with 90% summon resistence (bottom floor of first bonus dungeon) or use a Syphon Ring (stolen in the third bonus dungeon, but save first)), but could actually work. The chance of Death Breath killing an enemy is related to your behead chance. Now just get a good Devil's Lapis so you can uncurse and improve that Neck Splitter. Note that the chance of death from this breath does not decrease if you use it multiple times.

In your file I saw you have most of them multiclassed from casters.

I think that's quite important to note, as you don't mention Alchemist in your setup, Their usefulness is quite situational, but their spells can quickly change the flow of battle. + They get AP bonus depending on level, which is quite useful for enchanting gear, but I am afraid you don't get that capability if you multiclass away from Alchemist.

if you notice, I actually had two alchemists in the save file: one I beat the game with and one I created later in a different race. I choose Hotlet so I could influence the flow of battle sooner without having my leveling slowed down. One problem with Alchemists is that Magic Essence doesn't work on Alchemist spells.

It's worth noting that the second alchemist originally had Song of Healing, but I later edited her to give her Find Treasure and gave Song of Healing to my thief. One downside of giving the thief Song of Healing is that I can't use it while stealing.

I should also point out that Rafaireed is really only useful on Clerics and Bishops at this point (a Lord with the Holy Saber only heals around 300 points regarless of level). Hand of Kindness benefits weak healing spells the most due to the way it works.

One other setup that could work that I forgot to mention: Dwarf Cleric with Chi Wave. One of the downsides of Chi Wave is that it doesn't benefit from Physical Attack Power Up, but Clerics don't get that ability anyway. Just make this character male (because the game is sexist and doesn't let female or third-gender characters use the Hekaton Hammer (strongest alchemy-compatible hammer)) and give him a Hekaton Hammer with boosted damage.

One more thing: All of the really good weapons are either no alchemy or cursed, but not both. This makes Devilish a good race for some setups, even without the Spirit Pact bonuses.

By the way, take a look at my Werewolf Archer, who I have not class changed. Notice something a little odd?

Well, he is a Lv. 1 Bishop, who should have 3 lv. 1 Mage spells at that level, but he has none.

I am not pointing at low stat as oddity, because it is probably expected. Even though I don't have summoner and Spirit-Pacted monsters, that one Ninja from one of the quests, has very low stats for being Ninja (he is in attached pic)...

Btw, what is the Age limit for Devilish race? I guess 9/9/6/10/9/7 are racial minimum stats (and thus go to 19/19/16/20/19/17)?

Actually, the oddity is that, if you look at the Werewolf Archer's bestiary entry, it clearly looks like it should be a Hunter. After all, it has pursuit and is armed with a bow. Yet when you Spirit Pact it, it becomes a Bishop. (Note that it still has its 25% behead rate)

According to RACE.csv, the age range for Devilish is 0 to 400. For Magic Doll, 0 to 100. For Ogre, 15 to 60. For Goblin, 5 to 40.

All Spirit Pact monsters start with racial base stats. (Calling them minimums is inaccurate because the stats can drop below at level up.) The Mysterious Child is very much like a Spirit Pact monster, complete with, I believe, the inability to use Innocent equipment.

Maybe later I'll post some details about Spirit Pact.

Well, I attached bestiary entry for child, he looks to be the only entity so far who has Fear status (in Bestiary). Unlike other NPC entries, this child also has quite impressive stats (and he starts as !Neutral! Ninja) and he has Ex-Skill "Imitate" which he loses on becoming party member. I think there are serious reasons why game doesn't give you Spirit-Pacted monsters with exactly same stats and gear as shown in Bestiary :)

Also, gotta catch them all for monster and item encyclopedia ;)

I wasn't that much excited about Innocent gear by looking at its stat, perhaps I am missing something, but a lot of items look much more powerful than Innocent stuff. So I could live with Spirit-Pacted characters not being able to equip it.

Apparently, the most powerful weapon, the Mirage Lance, is Innocent only. The problem is that you have to steal it from Ibag Tower's 20F floor master, who is level 1249 according to the Japanese wiki. Additionally, third-gender characters are unfairly excluded from being able to equip it.

There are a few other innocent only weapons, like the Skulogy and the Unicorn Horn. There's also the Bicorn Horn which has an unusual value for the "Innocent only" flag in the csv file. Most items are 0, Innocent only items are 1, and the Bicorn Horn is 3. (Bicorn Horn is a rare drop on the last 2 floors of the first bonus dungeon.)