Installing macOS High Sierra Onto MacPro 5,1 (cMP5,1) Patience Required!

Retracing all my steps to install a fresh macOS HighSierra on my cMP5,1 2012.

Bought a new SSD, stuck it into the Optical bay and connected it to the second Sata cable.

Emptied internal x4 Drive Bay, 16GB RAM, Radeon 5770 stock, nothing else connected but Apple Keyboard + generic mouse.

I made a USB High Sierra installer and started the computer, zapped the PRAM, it started from the USB and loaded the installer fine.

I went into Disk Util and erased the SSD using APFS. [***Do not do this! Read on!***]

Got the Firmware Update Required window:

Clicked onto Shut Down button... Nothing happened.

Went to the Menu Bar, clicked onto the Apple Logo and Shutdown from there.

Pushed and held Mac power button, LED flashed, got the long Beep, computer restarted, but no Firmware update happened.

Again got the Firmware Update Required window... What the f*^%$?

Again clicked onto Shut Down button, nothing happened.

Again went to the Menu Bar, clicked onto the Apple Logo and shutdown from there.

Again pushed and held Mac power button, LED flashed, got the long Beep, computer restarted, this time it went into Firmware Update (fat update bar instead of thin one.)

After 5 min. the computer restarted by itself, Sierra installer loaded.

Clicked Continue, then got a window "To download and restore macOS, your computer's eligibility will be verified with Apple". What???

Went back to macOS Utilities and turned on WIFI and connected to the internet. Came back to the same point...

I canceled, restarted, clicked again on install, this time it didn't show this window, go figure. Went to the installer, but it DIDN'T LIST MY SSD in the disk selection for install... !! Arrghl!

Hence do not format your SSD to APFS prior to install.

Went to macOS Utilities, Disk Utilities, tried to erase/reformat the drive to no avail (could not unmount it, and I could not see it to force unmount it.

Shutdown, removed the SSD, went to a second computer, erased the SSD, this time formatted GUID/macOS Extended.

Put it back into the computer, started again, into the installer, and bingo!

Selected the SSD and started the installation at last!

15min. later, booting into High Sierra. Success at last!

Disk Util confirms that the SSD has been erased and reformatted to APFS as part of the installation.