Please Help!

I've recently purchased an Audi A3 1.9TDI Sport 03 Plate.

Upon purchasing I noticed that there was no Audi headunit in vehicle, only a cheap CD Player, would it be possible for someone to help me for the following:-

1. My other car I have is a VW Passat 05 Plate, I've replaced the original headunit/cd changer with OEM with SatNav:

a) can I use this VW Headunit in my Audi? If so where can I get an adapter to plug Audi Lead In VW Headunit?

b) If i purchase an OEM unit with Bluetooth etc... what leads / adapters do I need?

c) Where can I purchase a used Audi Concert CD Player?


Thanks for your Help