Forget the rental car advice. I'm sure you and your buddies are going to be drinking. If you really don't care about the accomodations, check out the Westward Ho. You can get a 3 bedroom suite with a living room (or a smaller room) for very cheap. It's located next to Stardust (good sports book and Tony Romas for ribs) on the North end of the strip. You can walk to a lot of places from there.
Check out the Flamingo and Imperial Palace for cheap rates as well. These are centrally located, otherwise you'll be spending the room-rate savings on taxis.
As for the 4 ppl/room rule, Vegas is like most places. If you give them a reason to enforce it then they will.
If you have 6 guys in a room, it will probably be a mess; it would be nice if you would tip the maids.