I've done a similar thing in the past where I forgot both the email and password I used. Contact steam, give them all the information you can for your account (STEAM ID, In-game name, and (hopefully) have the CC information available from when you purchased the account). The person I worked with got it back to me in under a week (mostly due to slow communication), but overall it wasn't difficult. Be sure that the email you do send them is one that you have access to (forgot this tidbit which added more time to my account recovery ).

As for level transfers, I could speculate that it probably won't happen (or rather hasn't happened in the past), but that's all up to clan on how they want to handle it.