I believe the earliest you could register your pre-order code was July 21st. So if that's when you registered, you'll probably be good to go on Dec 13, barring any technical issues on their end. They said they'll start sending emails once early access starts -- no advanced warning. There's been some good discussion on the forums from the devs about their logic:
http://www.swtor.com/community/devtracker.php
I don't have a guild yet/ Thanks for the invite offer. Let me know which server you end up on. BioWare is supposed to be sending out emails to those with guilds already registered before early access begins, so you should be hearing from them soon.