The E36 M3 doesn't really need much in the way of upgrading to be competitive. You could run in B-Stock just fine with relatively few mods.

As for a hatch, their low equipment level kind of limits them in Stock classes. I think most of em don't even have sway bars. I'd want to run in STS with a hatch.

These are the rules and classes and stuff, which should give you an idea of what goes where and how much you can change: http://www.moutons.org/sccasolo/