With all that's being discussed I wonder how this will turn out in online play.
I know your having a balance system in place, as was mentioned, 2 level 1 n00bs can take on 1 level 2 guy, but how will the wizards and what not work out. I've played games where, a higher level guy usually doesn't have too much trouble dispatching lower level people even if they are working in a combined effort. That's my only concern with the system now that Darvin hasn't mentioned (Or has mentioned but I did not read).
Other than that, what has been worked out seems like a solid method of ensuring sizable magic battles, but will there a way to automate some spells so it doesn't over burden the player while he's trying to fight off units with his regular troops and counter spells at the same time. It may not seem like much, but half the spells in Warcraft 3 I never use because I just feel like I don't have time to switch to my spell caster and still fight effectively.