depends if ecu is immobilised or not. pre-95 arnt, post 95 are. also, does your car have an immob, if not and ecu has one, nbeed to add the wiring and transponder box + reader coil from around the ign lock.
if you car has an immob, you can rematch the new ecu to your existing key + box with vag-com. Otherwise you need to get a matched transponder box + key, then you can match. if you just have a transponder box, only VW can code you a fresh key.
if you can get a matched ecu, key and box then no need to mess about, just plug n play