I would say you should decide on a Band Leader, even though you don't have a singer yet. If you have a designated Leader, you'll be less likely to just waste time when jamming, and you might actually get something done. Then, once you get a singer, you can always transfer the Leader-role to that person.

No matter what you do, though, you'll want to keep the songs you already know as a band rehearsed, so you don't have to go through the trouble of re-rehearsing the songs :)