A Solution for stack issue
If we limit attack and defence capacities for stacks it will solve calculatin troubles.For example we order 50 single stack to attack another 50 stacks, in this circumstance (example) only our 5 units will be able to participate the battle then they will fight only 5 enemy units.
@Schulz There are number of A&A style games that limit the number of dice rolled in battle, often by unit type. This tends to result in battles of even attrition, which is realistic for the Gunpowder era. Much the same effect could be achieved in the current engine by using stacking limits.
Stacking limits a bit different thing. In this way you can lose your territory in a round while defending whereas in my proposal it won't happen but still great feature.
There is a way to do what you are suggesting.
It sounds like you are looking to create a rather complex map. I think the best path is to start testing unit and support attachments on your own, to see what creative ways you can find to implement some of your desired features.