Great to have you! (team name being your name is perfectly fine)
Posting to twitter is absolutely great, and we will be using the hashtag #gdnjam. however to be sure you receive the participation points for posting the screenshot, when you do make a screenshot post, please be sure to drop by the competition thread(NOT THIS THREAD, a new thread created at the start of the competition), and be sure to drop us at the very least the link to your twitter post.
If you aren't sure what the theme will be yet and you're interested in some ideas, I compiled a list of Ludum Dare themes into a simple HTML page you can open in your browser. All 5 rounds for each Ludum Dare from LD 22 to 31 are in it, organized in tables showing the scores people gave them during the voting. There's some simple JS that makes each table fold at the press of a button, and there's a button that gets a random theme from a random table and shows it to you.
I put it together a while ago to help spur on ideas for games.
If you want it for some extra inspiration, I could PM it to you.