Any suggestions on rules I could use? - at this scale, I want something really detailed and characterful.
May I suggest Fistful of lead. You can make it as detailed as you want.
Just make a list of actions that take one move (e.g. kneel, dive for cover, walk)
and another list for actions that take longer (e.g. stand up from lying down 2 moves,
reload a bolt action rifle 3 moves)
You can also keep orders, as we used to do for Western Gunfight skirmish in 54mm,
e.g Move 1 Walk
Move 2 kneel & aim
Move 3 shoot
etc.