Multiple questions with multiple scenarios.
First of all, the coordinate input while driving and DVD playback that is viewable from the driver's seat is illegal while in motion in most states.
As such, discussion of these isn't allowed on the forums. I'd check the laws first, then with a car audio installer.
There isn't a screen kit that I'm aware of that is designed for passenger-side dash installation. That will be custom fabrication all the way. As far as interfacing w/ the GMX550 & nav system, they both need to have additional video outs. Check your manuals and/or with the installer.
The LCD kits for Yukon are probably meant for in-dash installation and would replace your GMX550 unit. Without links for reference, nobody could say for sure.
If you want to install a PC of any sort in your ride, it's advisable to start reading some FAQs and looking at other resources such as installs to get an idea of how to accomplish your goals.