1. Rated Battlegrounds are broken down into three brackets. 10v10, 15v15 and 25v25. These brackets rotate weekly and can be viewed in-game via the calendar by activating the battleground holiday filter.
2. Players must create a raid with the full number of players required for the current bracket before entering the queue. Any level 85 player of your faction may participate in the battle (regardless of guild association).
As I've mentioned before, I think there are two main types of group content: transient and extended. I think the current design of rated battlegrounds falls in-between the two types, and thus is more awkward than it needs to be.
Extended content works best when you have the same team each week. Where you work together as a team and gradually become better and better. Things like raiding and Arenas. However, for rated battlegrounds, the size of the team needs to change from week to make, making it extremely awkward to have a consistent team. One week you go with 10, the next with 15, the next with 25. It's a scheduling nightmare. You'll have to do substitutions and all sorts of shenanigans to get everyone in the guild their full quota of points, if you approach rated BGs from an extended content point-of-view.
From the transient side, there's no automatic group creation. Again, I believe that automatic group creation is a killer feature for transient content, that transient content is essentially crippled without automatic group creation.
With this design, rated battlegrounds will become like pugging raids today. However, if you think that Gearscore is bad today, you are not prepared for the hell that will be rated battlegrounds. Lose a game, and recriminations will start flying, even if the team that won was simply better. Those the group leader sees as weak will be kicked from the team after the first game, and the next 30 minutes will be wasted as the team lead tries to find the perfect current "overpowered" class with the best gear and rating possible.
Rated battlegrounds seem perfect for an automatic matching system. Just match people of similar rating together, and let them fight opposing teams of similar rating. Transient content should be approached in a transient manner. If people want to queue up with groups, let them, but the differing battleground sizes will always make that hard to do consistently week after week.
Creating a successful Pick-Up Group for a raid right now is a time-consuming and frustrating exercise. I'm not sure why Blizzard wants to use it as the model for Rated Battlegrounds, especially when the automatic group creation of the Dungeon Finder seems like a far better path.