I like keeping my config.plist as clean as possible and not fiddling with it much, so I was more than happy to temporarily remove my GPU to get the upgrade process working.
Just reporting in to anyone with the same issue: after removing the GPU and booting back into the Install partition from Clover w/ my Intel iGPU, I was able to get past the WindowServer error and complete the installation of High Sierra. I then continued on into my newly updated 10.13 install, installed the updated Nvidia drivers for 10.13 and then reinstalled my GPU onto the motherboard. It's running along just fine now.
I also just want to report physically removing NVidia card (GTX-1070) works to get pass the installation. Though, I had my own challenges with ACPI->DSDT's. I initially disabled all renamings, and after passing by the WindowServer and installation, I failed to boot. I mounted the Nvidia again, and enabled GFX0 to IGPU rename, also didn't load FakeSMC.kext this time, and it booted.
Then, the usual update of the NVidiaWeb and CUDA.
Everything works now, audio, facetime, all the works
Thanks for your time and effort, everybody!