Just to interject, part of OP's desire for answering this questionw as born out of wondering whether to wait or not before creating the character, but I remember being told that it was announced that you needed to have certain classes already levelled in order to unlock DRK. I never read this on anything official so I'm not sure if somebody has a source but, if that's the case, you really want to make your character first, and then swap if you want to play DRK right away. If I'm wrong, then my post is completely invalid.