you dont really need to get the hu professionally installed, but if you are a millionare you could just give someone $100 to fit ya wireless while you sit there and drink beer or something.
I dont know much about comodores myself, my wife has a vp calais wich still has the original hu (these are the same as some mercedes benz), I have added a dvd player in the pocket under the hu, mistake I made was that the disc touches the shift knob when its in park.
I never really have much to do with modern cars, I like my 50's cars but a guy I was working with once asked me to fit a dvd player to his 2002 prelude.
I told him I would if he shouted lunch at maccas wich wasnt a bad deal becuase I basically just took out a pocket and srewed in the dvd unit using the screws and mounts for the pocket with no cutting or drilling, I soldered up the power wires and while doing it he noticed I use heat shrink tube and asked if I could re join the wires from his recent STRATHFEILD instaled poineer hu, a deal was made with the meal now being large and a sundae added.
You could probably buy a adapter from supercheap to just use the factory harness and buy a single din hu to keep it all basic and easy without cutting any of the factory harness.
A friend of mine had a immobilser installed in his fe ute with central locking, they ran the wires from the edge of the door trim and into the kick panel when there were two safe ways to run the wire invisble, they also charged him for their crappy ideas and work, I fitted central locking to my FC, it cost $25 for four doors, I then found a remote immobiliser at k mart on clearance for $44,and wired it to the central locking wich gave me a imobilser for $69, I had fitted some power window motors I found in blubird doors out the front of the scrap metal yard, there was a spare output on the immobilser remote for a boot release so I wired it to the drivers window so when you hold the two buttons down the window goes up. I then added a cruise control kit witch was on specail at auto 1 and come with a dummys guide installation video, point is you can do heaps more with little money and have it all how you want it if you do it yourself and you dont have to be a mechanic, trimmer or auto electrician, I am a car washer.