Hmm, following along, even after making the edit for the resolution in the bios, QEMU just gets stuck at the UEFI Interactive Shell rather than boot the HighSierra.iso.
Edit: Never mind, doing this on unraid. appears for whatever reason the qemu_commandline portion got removed. Editted the XML version again via the gui and resolved that. But now I get down to two lines past the Identify Device checksum not implemented, and then I get garbage text with a circle with a line through it.