Yes, you have to tap pin 6/16 on the vehicle side of the harness because they aren't carried through on the aftermarket harness. So either cut the wires or use taps.
Get the Axxess ASWC working - All buttons
For the camera, it all depends on how you're going to mount the camera and where it fits. There are many different models that work in different spots. Here's the links I used for guidance but I pretty much used the knowledge from these threads to figure out how I was going to make it work with my camera.
BTW - I found all this stuff by using the search. I am sure some people would jump on you for not searching especially since this info is readily available.
Install: Back Up (Reverse) Camera
DIY: Kenwood DNX6140 installed in my 370Z with Sirius and back up Cam (AK370Z)
Nissan 370Z Forum - bpd138's Album: Kenwood DNX8120 Installation
back-up camera w/ kenwood