take the ECU to a tuner, or send it to one and have the immo defeated. one less thing to worry about when the car stalls or doesnt start for no apparent reason. If you want the added security of the Immo, just wire in a hidden kill switch.
Immo works by checking if the instrument cluster, ecu, and key all match. If they don't, you'll get 15 seconds of running before the ECU shuts the car down. It may also check the engine, but that I'm not sure of.
Beyond that the 2 harnesses should be basically plug and play since they are both mkIV.
Someone else should be able to answer better if an AWW ecu will work with an AWP motor. I don't see why it wouldn't.