The top 1,000 players will earn an exclusive Vanquisher title for their live realm character, and all players will receive access to an exclusive level 90 Arena Pass realm after they upgrade their account to Mists of Pandaria. What's more, players who participate in 50 or more rated Arena Pass games on one character and with the same team by the end of the six weeks will be eligible to receive the Armored Murloc pet for their live characters.
You can create up to three level 85 characters, all of which will be started at level 85 with a "hefty sum" of gold, parachuted in to a starting zone. Once you have your level 85, you'll need to get on board with a 3v3 team, which, as on live realms, can have up to six players on their roster.
The first two weeks are for practice, to allow players to meet, form teams, and get some matches in that won't count toward their eventual ranking, although teams will gain rating as normal. After the first two weeks, all ratings will be reset to zero, and for the next two weeks, there will be a -150 rating penalty for team roster changes. Teams will build ranking from the third week until the end of the six-week period.
In the final two weeks, rosters will be locked down and no changes will be permitted. If you want to change team rosters around in the final two weeks, you'll need to start a new team.