iATKOS Inside: Every option to move from Sierra --> High Sierra (or Mojave) is not working.

Every option to move from Sierra --> High Sierra (or Mojave) is not working.

I have a stable Sierra installation that I've been using since shortly after Sierra came out. I'm trying to move to High Sierra.

If I create a bootable install USB stick with High Sierra using Unibeast, it doesn't show up in my boot options when I hit f12 upon startup. The computer recognizes the drive and its EFI partition normally when I'm booted into Sierra, but not the boot options menu.
If I try to run the "Install High Sierra" app, it wants a password to install a "Helper" application, then says it will restart a few times during installation. It restarts all right. Once. And when it restarts, nothing happens. It just boots Sierra normally and sits there indefinitely. I have uplugged all other drives and made sure it is auto logging in to the only account created on the installation (obviously the admin login). Still nothing.
Out of desperation I tried to install Mojave instead. The installer application says "click to continue" from the first screen, and when I do, it sits there for 30 seconds and finally gives me an error: "Downloading installer information to the target volume failed."

I'm using an old-ish 64 gig SSD which shows no signs of failing. It still has 18.5GB of empty space, so I'm not just running out of storage.

Any suggestions for how I might get to High Sierra are appreciated.

I have posted more details in a thread on TonyMac, including my machine's specs:

Every option to move from Sierra --> High Sierra (or Mojave) is not working.