I can also throw out buying from crutchfield.com. That's where Mike bought from & was able to call them for help when he had a backup camera connection question. Great customer service. Beyond that, Mike's used the info on this thread plus messaging others who have done the install themselves when he needed clarification.
Currently he's working on installing the backup camera (the waterfall was out because he was hoping to route the wiring through there, no dice so it's going along the interior passenger side, under some of the plastic), & getting a good ground connection. Microphone is going above the rear view mirror, he ran the wire through the A pillar. Steering wheel control hook up is next on the list. GPS is picking up its signal using the OEM antenna, tested OnStar last night & it's also working.
Not a fast at home project - perhaps a little longer since he chose to solder together a number of the connections - install work started last weekend & he's been working an hour or so on it each night during the week. He's familiar with electrical work so that helps. And obviously a lot of the car needs to come apart ...
Lucky me - he gave me the car to begin with and now he's giving me an upgrade in it!