After multiple attempts, I was finally able to complete the install on my ASRock X399/1950X/Sapphire RX590/48G RAM. What finally seemed to work was the following:
1. Installed the Latest X399 Bios (3.50)
2. Formatted the new drive for MacOS (SanDisk 1T SSD) on my Mac, since formatting the drive via the install process did not work.
3. Disabled Boot to the SanDisk 1T SSD until I was able to boot from the external drive.
4. Installed Clover on an external USB Drive (instead of a USB Flash Drive). Also was much faster.
What is not working yet:
1. During boot up, the screen goes blank. But if I hit the enter key, then MacOS will boot
3. Sound via the DVI port - the sound option shows multiple DVI options
I will try the plist fix per the recommendations of others on the forum.
Thank-you all for your posts, and useful information.
This was the latest Mojave
Bios 3.5 did not play well with windows
I switched to bios 3.2 which works with both windows and Mac OS
I disabled over clocking as well