-Player vs. Player
Rated Battlegrounds
We keep a lot of players in mind when designing these types of things which is why we want to make it easily accessible. The guild you are listed in has a rather large number of people and the guild leveling/achievement system will help support this. Being in a guild like this, it likely won't be difficult to find a few guildies to put together a team and hop in the rated BG queue. There will still be non-rated BGs much like they are today if that suits you better.
-There likely won't be detriments for losing rated BG games, but the increase of rating for winning. (At least when you first get going in them). Yes, you need to win to get rewards. Rated BGs aren't meant to be a way to just casually and aimlessly get the best PvP gear in the game, but to reward those who compete (and win) on the grand scale of battlegrounds. (Source)
-Joining Rated Battlegrounds
This was just mentioned above, but I'll reiterate just for the sake of it. You need to be in a full group to join the rated BG queue. The team can change every week, between every match, whenever you like. The rating you receive is personal and not team-based so it doesn't matter who else is in the group. (Source)
-Rated battlegrounds are designed to give you the exact same type of gear that you can earn through doing arenas but through a battleground environment. The idea is that you don’t need a permanent team as you do in arenas, but you do need a premade team.
If the rated BG that week was WSG; then you just need to queue with 9 other people. You could change out those people for each match since you earn rating on an individual basis.
The rating gate (since you don't ever lose rating) will basically be your ability to get 9, 14, or 24 other people who want to play with you. Shouldn't be a huge issue when everybody first gets to 85 but a few months in you'll see stuff like you do today with ToC raids (5700+ gearscore mandated)
-This was just mentioned above, but I'll reiterate just for the sake of it. You need to be in a full group to join the rated BG queue. The team can change every week, between every match, whenever you like. The rating you receive is personal and not team-based so it doesn't matter who else is in the group.