@Stork Thanks so much for the reply.
I went and did the lot from scratch again, you know, just to be sure. And everything's good, I am in High Sierra.
Ran Multibeast, all good.
Note on the plist file: out of the box, it was already set as per your instructions, so I left it alone this time (checked it in PlistEditPro - thanks for the tip!).
Where I have come stuck... apfs.efi
The version I have is what came with the latest version of MULTIBEAST (at startup it say Clover is at 4458).
I have checked the path to make sure EFI is showing ('mount' in terminal) and it's as you outline above - /Volumes/EFI/, so looking at the EFI mount, /Volumes/EFI/EFI/CLOVER/drivers64UEFI/ is the correct pathing.
But when I run the command, it says 'No such file or directory' despite the fact that it is clearly there.... So if I try to run the patch, nothing happens. When I run the ls /Volumes/EFI/EFI/CLOVER/drivers64UEFI/, it also says it's not there!
Maybe this is the cause of the angst?
UPDATE: I ended up restarting without the above patch and everything worked ok- system booted into OSX. I then installed the Nvida drivers as per the guide and after restart it went back to not booting as per my first post
UPDATE II: I reinstalled from fresh
again (wiped disc etc.). Did everything up to the apfs.efi but this time reinstalled Clover from RehabMan's installer and rebooted. Success and I got it to boot into OSX via the USB (was not able to do this previously). I then ran EFI Mounter and terminal picked up the EFI path. Ran the patch and checked the last update time stamp on the apfs.efi, all good, it updated. Rebooted and again via USB, and yep, booted into OSX.
Now restart with the USB out. Into BIOS, reset the boot drive and go. Progress bar to 90% and then Nop!
USB back in and boot from it. Yep.
Looks like I have the won't boot without USB issue. Looking into it now. Otherwise, it all seems to be running fine
UPDATE III: I got it to run!
Using this simple fix got the system to boot into OSX without the USB. I also had an additional EFI mount on the second disk (which I originally did the install on), so I deleted the EFI folders on it.
What's not quite right?
a: I can not get the BIOS to boot to the SSD directly, which means I have to go through the whole enter/exit BIOS thing every time. Once in Clover, I have to manually select the boot disk, rather than it doing so on countdown, though this last bit is not a big ish to me at all.
b: And this may be something or not... I did the sound patch (last step) and restarted but when I plug my headphones into the green port, the system does not see them at all, hence no sound. Do I need to use a powered system to have it picked up or should it see the headphones?