yes
Rock Band 3 supports guitar, bass, drums, up to 3 microphones, and the all new keyboard.
Yes...
Yes.
Yes, you can use Rock Band 2 equipment for the Rock Band 3 game. They are backwards compatible with the game.
no.... sry! D:
Yes, you can use the Rock Band 3 drums with Rock Band 2. The Rock Band 3 drum kit is backward compatible with previous Rock Band games, allowing you to play Rock Band 2 with the newer kit. However, some features unique to Rock Band 3, like the keyboard or pro mode, won't be available in Rock Band 2. Make sure your game console settings are configured correctly for optimal performance.
Yes you can use The rock Band 2 set with Band hero. The Band Hero (Guitar Hero) Drum set has the Orange cymbal, which is one more pad than the rock Band 2 drum set. Fortunately Band Hero Detects that and modifies it songs for the Rock Band 2 Drum Set.
In my experience, any guitar worked for both Guitar Hero and Rock Band in the majority of the games, including Rock Band 3.
Yes, you just will not be able to use the Pro Mode.
probably not
Yes.
yes they will but you will not be able to use the pro modes with the old controllers