As you noted getting a good installer is a great idea. I do my own mainly because I like working on things but the shop I have dealt with for about 12 years is great. They don't BS and told me exactly what I needed to put the unit in my HHR, even to having to cut out the back of the plastic dash are where the unit sits. As far as my car thinks, it still has the original stereo in it.
On mine I did the "bypass" so I could have videos play while the car is moving and the shop said they can not do that as it is a liability issue and possibly against the law. My dogs love watching videos when we take them to the beach and lay with their heads between the seats! Here is what mine looks like with a ZZ Top video playing.
