I would rather avoid having one unit represent multiple soldiers. As to one cohesive regiment or company, I think 5-10 units is plenty. I also think it would be nice to, early on, recruit only one at a time, whatever, although later on when you have the proper requirements, able to recruit all 10 at one time.
although it would be nice to have larger unit sizes, really the max we need to get would be 50, imo, and that would be for something quite massive, like skeletal horde, or somthing. (maybe angry mob? goblin raiders?)