Since Fosgate was sold, I'm no longer a fan of their products produced now. Much like what happend to PPI back in the day.
I have had experience with their products produced back in the late 90's, but nothing since around '04 so I cannot comment on their quality, performance, ect...
For what size amp, and what subs, that will depend on your goals and enclosure. If you're running stock speakers, I don't see why a single 12 or even a single 10 (of good performing drivers) wouldn't work in a medium sealed box...Though I don't know if the Fosgate P2 woofers fit in that "good performing driver" catagory, I've never used it.
I do have some subs by CSS; The SDX-15's, but they're 15"
http://www.youtube.com/watch?v=ODm5G4nAbOMThey also make some SDX-10's that are...wait for it...10" One of those should be sufficient in a medium sealed or ported enclosure.
Regardless of the sub(s) you pick, if going ported, you can get by with a bit smaller amp.