You will not be able to cosign on the loan without your name on the purchase contract and taking title. In California you can quit claim your interest back after the sale closes, but I am not aware of a lender that will let you cosign and not take title. I am working on this situation (have an escrow open) with a buyer right now. The co-signer is required to be on everything.
There might be a lender or broker that might figure out how to do it, but I am not sure if you do, that it will be above board.....
if your name is the loan and not on the title you are not the owner of any home. However your credit will be affected. Your first time home buyer status should not change. To confirm all of that I like to refer you to my lender who also give financial advise. Please call Dave Gaylord at (949)939-6011.