[Aerich]

It's fine. I agree with ZFR's comment re druids. Regarding character #2, I'd make it a straight multiclass F/Cl or R/Cl. Reason being, the cleric lacks offensive punch and yet has some good self-buffs that seem wasted on a single-class cleric. 1 attack/round just doesn't cut it, and the cleric won't be healing every round.

I wouldn't put axes and greatswords on your dwarven fighter, because both weapons do slashing damage. Use flail or mace instead so you can crush skeletons and other slashing-resistant creatures.

Re: the mage, either option is fine. I'd go for the extra HP myself, but if you're playing on normal difficulty level with 6 characters, it will slow up your mage's advancement.

I'd say you need a thief of some sort, purely for convenience - I've done the game without, but it's not fun and some parts are downright painful (Dragon's Eye comes to mind). Never use a single-classed thief in IWD. The F/T multiclass is a competent archer and advances fast enough to cover off all the thieving (especially as you have a bard to cover pick pockets). I don't think it really matters what race you pick for it, although I would steer away from dwarves (a "ceiling" of 17 Dex). There's a good helm for halflings or gnomes only, but elves get +1 with bows and swords, which is always useful.