The only suggestion I can give you is be very gentle while removing the original radio. By now, the plastic used in these cars are brittle and can stress crack or break easily, more so if the car stood in the heat a while. My first 780 I bought used, came with a single DIN stereo installed. It used one of those “Stereo Installation kits” that are common now whenever you want to change a newer vehicle’s radio to a single/double DIN. Quite nice because it had the storage space under the stereo and looked great. I highly doubt you’ll be able to find one of those kits today so you’ll have to get creative.
The amps are pretty straight forward to remove. The wiring you can either bundle up and cable tie in place or you can deal with removing it which means you’ll be pulling some interior trim to get it out. OR, if you don’t care about it, you can clip the wiring down and out of sight. I removed the wiring from both my 780s so you know there is at least someone has a spare sitting around. At the same time, neither of my 780s had CD changers so I’m useless with advice there.