I have 'played' BG1 and 2 before, but never to completion.

I'm going to do so now, since I just picked both up off the sale. BGtutu and then BG2. I really like spellcasters and with the lack of cleric in the 'canon' party, I was thinking Cleric/Mage multiclass, since I just can't give up Mage either.

Could someone describe the big pros and cons for doing this for my first full playthrough? i.e. Final spell levels by end of BG1, mid BG2, etc...

In BG1, you will typically end up at the experience cap, which is 161,000 with the expansion. This means that you will end up as Cleric 7 (instead of 8) and Mage 7 (instead of 9). This means you don't get 5th level mage spells, but that is the only spell level you lose in BG1.

In BG2, the difference becomes more pronounced, once XP requirements start becoming linear instead of exponental. You won't get level 6 cleric spells until a single class cleric would get level 7 spells. (If you are using Jaheira, this won't be too much of an issue because she gets level 6 spells, and hence Heal, before a single class cleric would.) For mage spells, you don't get 7th level spells until a single class mage gets 9th level spells.

From what I understand, Throne of Bhaal typically gives a full party to about 6 million experience points, which is right when a Cleric;/Mage gets 9th level Mage spells.

On the other hand, Cleric/Mages do get one major advantage: The ability to put Cleric spells (which typically have long casting times) in sequencers and contingencies.

It is worth noting that, in BG2, there is a Cleric/Mage available to recruit early, right after you leave the starter dungeon.

There is. Jaheira is a cleric in respect that she gets cleric spells. There is also Viconia, a pure cleric.

She is squishy without care and thought, yes, but with proper management she is one of the most devastating characters in BG2. All she needs is the Belt of Fortitude (or potions), and Gauntlets of Ogre Power/Crom Faeyr, when she can melee with the best of them. You just need to be mindful of which armour you give her, because of her arcane spells. As for annoying, aren't they all?

Cleric/mages are pretty cool. There's a thing you can do with Project Image + Wish that gives you somewhat unlimited spells, including all the cleric ones. That and, as someone else had said, putting cleric spells in contingencies, makes this class a lot of fun. The only downside I can think of is the split exp.

I'll keep this in mind if I decide to pick her up in my next play through but having her in melee? I've never tried it but it is kinda hard not to balk at the idea considering how careful I had to be the last time I used her. Still, you know this game better than me so I'll just take your word for it that she can do melee with the right gear You know, when I saw your post, I actually did think about which NPC wasn't annoying in at least some way and was surprised how close to the truth you were that it makes me wonder how I missed it. I haven't used Cernd, Haer'Dalis or Jan in any of my play throughs so I can't comment on them but I think the only NPC that I didn't find annoying was Yoshimo. Maybe Keldorn too but last time I used him he didn't stick around for too long, I let him go back to his family.

Just remember that she's never going to be as good as a front line fighter, nor should she be considered a front liner, but give her Crom Faeyr and the Shield of Harmony, and you need never worry about Spirit Trolls and Golems (not counting Adamantine Golems) again. She is, and always should be a support character, but like Jaheira, she can mix it up when necessary.

One thing to note is that Mages (including Cleric/Mages) actually make good tanks in these games. Mirror Image, Stoneskin, and Protection from Magic weapons all allow arcane casters to avoid taking damage from enemy attacks, and if you are worried about dispels, there's Spell Immunity. As a result, low HP is really not a problem because you never take damage.

As for using Aerie (the NPC in question) in melee, that is even doable. Two casts of Strength can give her 18/00 strength for a long duration. One cast of Strength followed by Draw Upon Holy Might will give her even more strength. (Try putting DUHM in a Minor Spell Sequencer so you can avoid the casting time.) You could also have her cast Polymorph Self and then launch the DUHM sequencer after being transformed. (The downside of this approach is not being able to refresh Stoneskin, but at higher levels, you can use a Contingency for that.) Of course, this works for any Cleric/Mage (or Cleric/Illusionist) that you create yourself.

Another thing of note: Can't equip an item because of the strength requirement? Just cast Strength on the character and equip the item. Even when the spell wears off, the item will remain equipped. (This also works with items as well.)

P. S. If you want things to get really silly, use a sequencer to cast a spell like Spiritual Hammer, or better yet, Shocking Grasp, while polymorphed. This allows you to use human weapons while polymorphed. (In the case of Shocking Grasp, after you hit an enemy, the touch effect disappears and your natural weapons do not return.)

P. P. S. Using a certain cloak to turn into a rat and casting Armor of Faith (at a high enough level) can give you 100% or more resistance to physical attacks. Too bad the rat's natural weapons are weak (but if you use the previous trick mentioned...).