I would hazard that for getting the most benefit with the least, is to start with some broad band reflection control. I.e. two inches or greater fiberglass, even partial covering (or sectioning) is a good start. And don't forget to include some overhead of the mic(s) as that can be a hard path that can wind up being even closer than the walls.
As a home-recor', that's about as far as I'd care to step in this company.
