With so few points involved, you would indeed be only playing with a single division.
To be honest - I'd just stick with the basic rules. I've played perfectly fine with one Vs one division, and the game runs just as smoothly. I've done Carthage VS Republican Rome - and We kept everything the same, where skirmishers are ignored if destroyed for broken divisions. Ultimately, the game is much faster and quick, but it still turns out to be a fun game.
I also suggest trying the game without points at small sizes. It can still be as fun
Finally - if you want to just do a fight to the death, that might be better than the over 50% break rule - just so all units can be involved in the game
cheers!