@mitu - Thank you! I wasn't. I am now and the xrandr commands have worked.

You're not running into issues with building the N64 emulator mupen64plus? It's only happening on Debian Stretch (x86-64) but it could be my setup so that's why I'm asking. It's requiring a newer version of cmake than what's available:

/home/pi/RetroPie-Setup/tmp/build/mupen64plus/GLideN64/projects/cmake /home/pi/RetroPie-Setup/tmp/build/mupen64plus /home/pi/RetroPie-Setup CMake Error at CMakeLists.txt:1 (cmake_minimum_required): CMake 3.9 or higher is required. You are running version 3.7.2

On a PC, RetroPie will need an X server to run and you should have that functioning before starting the installation.
The dependencies are just a few small packages (libSDL mainly and a few other libs) and on a straight Ubuntu install the base RetroPie install should be less then 800 Mb. However, since installation on a PC will compile everything, quite a few -dev packages will be installed (mostly X related) and take space during the installation itself - you can remove them after installation is finished.
If you add more emulators, the RetroPie installation might take more space, but not considerably. I expect the ROM folder and the scraped artwork (video/images) to take (a lot) more than a RetroPie install. If you managed to get your base installation under 5 GB, I think the installation to be fine and still have space to spare. Make sure you have a supported distro - Debian/Ubuntu.

@MajorDangerNine I've not checked but I suspect you renamed important page(s), breaking any links to them from other pages and the navigation on our docs (and generation of). Would be wise to check before making changes like this.

Renaming pages is a bad idea in general since it breaks links to them.

Replace system.sh with this http://malus.exotica.org.uk/~buzz/system.sh and let me know if it works for you. Note that retropie-setup is not tested on Debian unstable, so some things may not build or run properly.