I've been using 10Gb network to connect to my NAS for a long time and it makes a huge huge difference. But, yes, in many instances, 1GBase-T is fine for file sharing.
On my Raspberry Pi, I just had OpenMediaVault installed on an SD card. On a PC, I'm sure a USB flash drive would be fine. Make sure to make backups of the USB flash drive.
You don't even have to pull the USB flash drive if/when you want to boot a different OS. Just go in to your motherboard's BIOS boot menu and select a different boot drive/device. I think on Gigabyte motherboards, it's spamming the F8 immediately after powering up.
For anyone interested in closure
tl;dr a fresh Open Core install of Catalina did the trick.
x OMV.
I installed OMV over the weekend. It was easy enough to install after watching a couple of videos. That's a big plus. I toyed around with it for a few days, but couldn't figure out how to set it up like I wanted, i.e. JBOD. I was only able to create shared folders, couldn't figure out how to set the size of them, and it seemed to require erasing the drive first, which wasn't practical for my setup.
x Windows 10.
I tried setting up a network with Windows 10. And I was quickly reminded why I dislike the Windows OS so much. Driver incompatibilities galore. Awful interface. Advertisements in the start menu!? A system update that tried to steer you into an Office subscription (it seemed mandatory, but wasn't), couldn't use the trackpad or bluetooth keyboard, etc.
✓ Open Core, Catalina
My last ditch option was to try and install macOS Catalina using Open Core, on the slim chance that the problem was the software setup rather than hardware incompatibility. More fuss and trouble than I experienced with Clover (and almost more than I wanted to deal with), but much to my surprise and relief, File Sharing worked.
A big plus: screen sharing between the two computers. A simple swipe on the MagicTrackpad let's me jump between the Mac Studio and the Hackintosh. The wireless keyboard and trackpad even work on both, like magic.
There are still some wrinkles that need ironing out, e.g. there are permissions issues with some of the drives; two network drives appear as attached drives when I click Mac Studio icon in a Finder window (which is great). The others are only visible in the Network folder (haven't yet figured out why).
Also, I still need to try and fix Sleep on the Hackintosh. It would be nice to have it power down when it's not being used and wake only as needed. [Not entirely sure if that's possible]
10G card?
And if that all gets sorted, I'll look into getting a 10G network card to speed things up. I'm getting transfer speeds of 60-70 MBs/second about half the speed of a hard drive and 1/10 the speed of an SSD.
I also need to look and see if there are any apps that would help run and manage the server, e.g. measure speeds, keep an eye on disk health, etc. It's a shame Apple discontinued their server application. (Supposedly many of the Server app's functions have been rolled into the latest OS, but they're scattered and seem incomplete).
Thanks again to everyone for the help, advice, and encouragement.