i think 1herotower per race is enough(for the time being)
List:
Imperial Guards:Ursarkar Creed and Jerran Kell (one unit)
Chaos Khorne:Kharn the Betrayer
Chaos Nurgle:Chaos Lord Typhus, Herald of Nurgle
Chaos Slaanesh:Emperor's Children Lord
Chaos Tzeentch:Ahriman of the Thousand Sons
Dark Eldar:Asdrubael Vect
Eldar: The seven Lords (i didnt know which one i should take)
Necron

estroyer Lord
Ork:Mad Dok Grotsnik (changed)
Space Marines:Blood Angels Commander Dante (thought Blood Angels are the most important)
Tau:Aun'shi
Tyranids: Dominatrix (thx v3ck)
ralle all ideas are good but i think u should wait with new races and more levels cause first u should improve the actual races then in the version after the next one u should think about more levels and after that at a new race but the thing with the obliterator should be made fast cause for its money it s not very good.
Yours
Robi