I like how armies are set up in Total War games, personally.

-Yes, one killer stack of 20 elite units was the best option on the battlefield, but getting one of those was expesive and took a lot of time. Plus, such a stack could only be in one place at a time, so even if you used your stack to lay seige to an enemy, they could move weaker, yet cheaper stacks around and hit you in multiple places.

-Multiple stacks could fight at once. Three 20-unit stacks could surround one enemy stack and destroy it. The balancing point to this was that there were not many situations where you would have several full stacks in the same place at the same time.

-Each "unit" consisted of 100~ individual soldiers, so even if it was fighting rabble, your elites are still going to take many casualties (especially in seige battles) unless you've worn down the enemy and fatigued them.Usually, if you were deep in enemy territory, you would be very far from your "core" and as such, it would be difficult to replenish your elites

-This makes the best plan splitting your elites between your armies and using them as reserve troops to back up your more expendable militias.

Not saying it's perfect for a game like this, but there are certainly some ideas to take home there.