There will be 3 playable characters in FFX-2. Yuna, Rikku and Paine. However to comphensate for this there will be "dress spheres" that you can get. This allows characters to change job class (also changes abilities and stats). The job classes that I can recall at the moment are White Mage, Black Mage, Gunner, Animal Trainer, Swordsman (or should that be swordswoman!), Theif, and Songstress.
Square-Enix's Japanese FFX-2 site has a lot of very good pictures and info, but it's in Japanese. I managed to find my way around it though! FFX2.com used to be a really good site for FFX-2 info, but they are currently undergoing a re-construction. And I think when they come back up again, they'll be full of spoilers, so I guess I won't be going there anymore.
I'm really looking forward to FFX-2. It should be a really awesome game, especially since I really enjoyed FFX (it being my second favorite FF game and 5th favorite all time game). My only qualm was with the "outfits" that they are wearing. I don't like the whole FF meets Tomb Raider look, and prefer Yuna's FFX outfit a lot better. And Rikku in a bikini! Oh well. I guess I'm getting used to it though. I do really like Yuna's songstress outfit. That looks really cool.
Abe Babe...