Raen Yrtham is my gamertag, you can also add me if you want, even though I don't play Q3A on the 360 that much - blame World of Tanks for that!
The 360 has KB and mouse support out of the box I think, don't know if the game supports them, but it's just a matter of trying a USB KB and mouse combo.
its pretty much dead online. it also does not connect to to pc or dc version. On the up side its the same as the pc version as far as graphics, FPS and server hosting for other xbox players. Unfortunatly I cancelled my xbox gold account since I usually play on the ps4 now