Street Racer, I was having all kinds of troubles and no kind of successes...then read your post thoroughly and found you were working with a later version of the BIOS firmware. So I updated and followed your settings carefully and voila! I finally got some traction...ran the High Sierra installer all the way up to the point where it hung on trying to trying to connect to the WindowServer and it exited with code 1...and after hours and hours it is still trying to run that service. I don't know what all that means just yet...but I am so thrilled with major change in my build and install. I am now going to search for the cause of this activity. Thank you for such a great post with all the visuals and clear communication about your success. This is a huge advance for my project!
And so...here are a couple of shots of the progress of the install (large image) and then where it hangs (2 lines of text) at trying to run the com.apple.WindowServer.541 service. The installer after left overnight, was still trying in the morning; so the process was alive (i.e. had not crashed and burned) but just not completing. This is way out of my league, but it is still a success for me...of sorts. So far beyond where I started. If anyone can decipher this, and has a clue of where to kickstart or correct this failed process, I would be grateful. Feels like I am close to a win.