Looks like you're making great progress, Eric. Keep the pics and narrative coming. They let me see what I'd be getting into if I had the courage to disassemble the cab of my new NX before I turned 25 hrs.
I'll be interested in what you finally decide on back-up monitor location. My monitor and camera won't arrive til next week (thanks again to 94Bullitt for the tip and links), so haven't thought much yet about where and how to mount. The NX series has a fairly sturdy polymer dashboard, with what looks like a pretty good mounting surface over the main instrument cluster. Might try the monitor there. Don't know if that would dampen or exacerbate vibration. Seems like it could go either way.
Interesting about not being able to drop the headliner. For the camera and monitor cabling, I was thinking I could run it under the trim down the door post, then under the heavy rubber floor mat. The mat has deep channels molded into the underside that look like they'd make good races for cabling and still protect it.
I'm curious about the back-up lines in the camera. If the camera comes with directions, perhaps it will say how they are to be used. The idea doesn't bother me, in fact they seem like they'd add known reference points that will be useful when backing up. I guess they could be a distraction when using the camera only for monitoring 3pt implements when driving forward.