If your car is pre-07, it'll most likely need a new gateway to prevent battery drain. Or you could look at getting an RNS310 which wouldn't need a new gateway. The only sure way to tell (without physically getting to the gateway), is to plug in VCDS and you'll get the gateway number from that.
If you don't have bluetooth, that'll need to be installed separately as well.
Do some searching on the forum for battery drain issues, and you'll pick up all the info you need.