An alternate idea for training and added lore opportunities.
Borrowing a page from Final Fantasy Tactics and other similar Tactical RPGs has the idea of missions for your characters. Set up a squad and send them off to lord knows where for a few weeks and see if they come back; i.e. Off-screen action.
You make a squad and send them off to some remote location (somewhere in the game world) and you can pretty much generate an adventure for them. Simulate up a whole nice adventure, maybe output a log of their journey, and in the process train them up military wise (to reduce the need for danger rooms and barracks). Sending them off for 1-12 months and they return with training, some loot, and occasionally (how the simulated adventure pans out) the dead.
Advantage:
Fewer units to track for a while, no need for physical tracking of the units for a while
Unlimited potential for building adventure stories they bring back
Another training channel for military
Chance to interact with off-map entities (maybe the evil Lich they fought got away and a few years later shows up looking for them? Oh Fun!)
Disadvantages:
More coding.
A possible opportunity exists to make the adventure modules external files so players can contribute adventure components.
It's more or less a
Pick Units
Pick Supplies
Send them Off
See how well they succeed.
Maybe they save a human village, maybe they sack an elf town.
Perhaps you have to build a tavern first, then inspect the tavern to see if there are any Adventures posted. If so go to squad->orders->Adventure. Then build a cart, stock it with supplies and set the cart to "venture off" taking the marked squad with them for how ever long the adventure takes. Then they come back X months later similar to migrants.