iOS social/multiplayer scope

I'm currently building a game and wish to integrate social and multiplayer features, but not totally sure how to approach this. In terms of functionality I want a player to log in and be able to add up to 3 friends who also have the game (via either facebook or some other means) and keep track of each others scores. The players must add each other before the rivalry is accepted. I'd also like the ability for players to send each other difficulty modifiers that trigger during gameplay (so if I send my friend/rival a bomb they won't be notified until it goes off in their gameplay, making it more difficult for them). You can see if your difficulty modifier has been triggered by your rival or if it is still to be activated.

Currently I'm looking at the facebook SDK but I'm not sure if this will support all this functionality. Can anyone tell me if it can, or give me any pointers on how to approach this/services I could use? Thanks.