When I DL the CS do I get all the kit, have to choose just one of the four, or will I need to start a new game to get the Stash?

You get all the stuff from all the packs. You get it all immediately upon loading your current file or starting a new game. It's good money right at the begining, I can completely clean Chet out, and still have a decent set of armor, a gun, and a grenade rifle.