Arie!!! But who else?

[Amergin]

well, you're obviously going to be the primary mage as you will get the higher level spells far sooner than aerie, so keeping imoen would be redundant unless you just love having spells as you main battle decider. jan is more than adequate for thieving; the fact that he's a multi w/mage isn't much of an issue as his and found items can boost his thieving skills. all you really need is a single class cleric and a tank or two. since you want aerie, korgan as tank is out so that leaves keldorn, valygar, and anomen. anomen has a crappy DEX but that can be fixed with some gauntlets or potions of agility, thereby filling both roles of cleric and tank. valygar can dual wield katanas and makes a great second line fighter, and keldorn's inqisitor abilities (and being able to use carsomyr) are a boon vs mages.

[StarVid]

I agree with what someone else said, you are pretty weak without a druid. I'd pick up Jah. You do have another option though, and it'll keep you from needing a druid or Anomen. Considering that you're picking a kensai/mage, I'm assuming you're looking for an ubermunchkiny PC. With that in mind, I'd go for the Human dualed Ranger(9)/Cleric. This is my favorite tank in the game. The only problem with this is that you have no contingiencies/sequencers (and I've always played a mage so I'm used to this), but you can still mess some stuff up. In short, on party formation:

Ranger(9)/Cleric, Minsc, Keldorn, Aerie, Jan, Imoen

or

Kensai/Mage, Minsc or Keldorn, Jah, Anomen or Vic, Jan, Imoen