How 'bout you can put in training slot lets say a whole stack together with comander/general, and then you need a couple of turns to recruit it, but then each army will be really important, and losing it could be a heavy blow.....
Like not "i recruit here one comitatensi, there 3 militia, there one sagitari, then bring one general.....
But this way let's say you need a lot of money and then you are recruiting a whole stack, not just one or tweo unit types. Whole stack in the same time, so lets say for example that Romans in Africa will have one stack, (not counting the town garrisons) and with it they need to fight off the Vandals....
So at the beginning it would be One stack (army) in Africa, one in Galia and one in Italy (and perhaps one in the Balkans...
Ofcourse this stacks can be retrained (alltogether agin, offcourse) in nany of the town which have some of this unity types....
What do you think people?