Hm . . . ancient vampires playthrough. not bad idea, but it`s possible you`ll have problems getting enough vampires to restock your army. I played this game for some time now (what an understatement
and rarely have found some reasonable amount of ancient vampires, to be useful before finishing quest for Mysticus and having chance to change normal vampires to upgraded version. On other hand solo BK or droid playthrough no problem since they can be found in almost unlimited quantities (BK from Moro Dark, or castle in undergroung in Montero, and droids almost anywhere on Montero in hordes).
And Warrior`s counterstrike not working with undead would make solo ancient vampires boring, even more since they dont get any bonuses like black knights, and crippled from lack of beneficial spells.
All in all, really unbalanced race to race up`s and down`s.