Please try to answer this question broadly... not just the question at hand. Will I lose my users, posts, etc, etc...
you will lose all users and posts. we don't care at all about backwards compatibility we are evil doers that like to kill all data and information out there.
The schema for BB comes from PhpBB which is fairly stable today, so your question on schema is that you will likely not have to do anything
Ok, I think you are kidding, but I have already noticed some changes in the user table, so I think I actually will have to drop all my users, and that you are evil doers.