Correct.
Like I wrote before, the macOS installer will upgrade the firmware. I'd install Mojave right now and check if can at least complete the install.
Yes.
So I went and booted back into Mojave using the USB stick I installed Mojave onto.......and now Disk Utility/everywhere else is suddenly not showing the internal SSD anywhere?? What the heck sense does that make? It's connected in just the same, machine has been untouched since last time I posted.....
To boot I just inserted the USB and pressed start...nothing special. Really don't get this...