I wish you could carry all the Kohan you find with you between missions, but honestly, I've always found a particular three or four that serve me well and just stick with them as long as I can. Also as a pro that's also a con, different types of cities (Council, Ceyah, etc.) have different types of units you can recruit. I know I said previously that there are some units that are just less useful...but no, there are indeed some that are useless. And some cities that are basically useless to hire from unless you're stuck with them. But that's part of the challenge I suppose!
And, no, the Majere you see in this game is not related to the Dragonlance Majeres, sadly. I'd love to see a Dragonlance crossover into anything, make my forever, that would.