1. 0-19 Newbie, 20-99 Junior,100-499 Advanced, 500+ Senior.
2. Those four plus VIP, Moderator, and Admin. (I think that's it)
3. VIPs I cannot recall too much about. I think they are only comprised of people who joined up before a certain date. (not sure)
4/5. Stars are the members rating, similar to movie, hotel or restaurant ratings. You can rate other members on their profile page. The stars shown is their average rating.