Do you absolutely need 2 wiimotes for 2 players? Or can you use GC contollers? Or a mix of both?

You can use a mix or just Wiimotes or just GC. But just keep in mind it respects the # the controller is synced to:

eg:

Wiimote on port 1
GC plugged into port 2

You will never have Wiimote on port 1 and GC in port 1, that won't work.