Personally, it occurs to me that armies don't really have any maintenance requirements other than some Siege weapons need stone to fire. Ie. Huge armies and they don't actually eat Food, need Wood to make arrows, Stone to sharpen blades & metals to repair nor Gold as the units will gladly die at the whim of the player just because they love the player so much.
If maintenance costs get added, I doubt maintaining a large powerful army would be that easy. Less so if the Cities and camps have maintenance costs added to them (with penalties for not maintaining them - ie. decay, reduced/no output and eventual destruction/removal, etc.)