Well.
Think of it as though each person was a lvl 12(ish) character with the leadership feat, and a decent leadership score.
Each player has to equip and organise the Followers they get into units for battle. (Each unit would be identically equipped for ease of combat)
If there is some interest then there would be a monthly budget they would get for equipping and paying their troops.
As for story and why they are fighting... I haven't gotten that far yet. Wanted to judge the interest first