I created the Mojave USB installer with just Mojave 10.14.4 and Clover 4961. I then copied the Clover folder from Post #2 into the EFI folder of the installer, renaming the original CLOVER folder. With this, I was able to successfully get to the installer. I use APFS and noticed after installing, that Clover did not see my installation, so I checked and found I needed to add ApfsDriverLoader-64.efi to the Drivers64UEFI folder on the USB drive. Then, Clover would see my Mojave installation.
After that, pretty much everything worked, thanks to the carefully crafted EFI folder by
tevenfeng!
In any case, my GPU is natively seen but I discovered that with that card installed (Sapphire Nitro RX 580 8GB) that I could not put the lid on the system! The GPU card is giant and too high to close the lid. That led me to try to get the card that came with the T5800, a AMD Firepro W8100, working. I had to edit some info.plist files to add the ID's for my card, but I got it working and can now put the lid on! And, W8100 is Metal supported, just not quite as fast as the RX580.
I also moved all the kexts (except FakeSMC) from the Clover/kexts/Other folder to L/E on my SSD using KextBeast. Some I didn't need (like the nVidia one)so I removed it.