Lucky for you the VSS wire is in the existing radio harness. I think it's a grey/black wire but don't remember off hand. Check out
AVIC411.com, those guys have all the tricks and answers.
The reverse wire gets tapped at the back of the fuse panel. It's a black/pink wire in an 8 pin connector. You may also want to do the parking break hack. See avic 411 for all those goodies.
I put the GPS antenna on the dash and it works fine. No need for all the extra work to mount it outside in the elements to get ruined.