I like where you're going with it, but I didn't quite understand what to do. Your idea is definitely going beyond what Stardock attempted to implement in Crusade. More interactive and not just "place your legions and see what happens".
That is my intention 
What to do can be seen by the text below the map, essentially:
- Place defenders' units (split in immobile defense artillery mainly to protect the capital and mobile legions)
- Place attacker's units (only legions). Placing attacker's units adjacent to a defense artillery means it's shot at while landing, reducing it's strength.
- Perform turn based battle (since there is no AI by playing both sides manually). Every unit has one action per turn, either move one field or attack adjacent unit.
- The map is generated randomly every time (press F5 if you are not content with the layout), on it the capital is placed (the purple circle with the black center) as well as a bunch of other "improvements". To give the player more to do than just attacking the capital there is the possibility to destroy or raid improvements as described in the text to the right of the map together with some descriptions how battle works.
I hope it's now a bit clearer what to do 