Just to add a data point, last summer I built a Ryzen based ZFS NAS and was hoping to use a RR 2400G w/ the ASRock AB350 Gaming-ITX/AC board (since it had confirmed ECC support w/ Zen 1 chips) as I had the same situation where the single PCIe slot would be used by a SAS card - plugged away, did research, talked to Asrock support, but sadly, came to the conclusion that there simply wasn’t any board out there w/ support (unbuffered ECC memory boots, but always runs in non-ECC mode). In the end, I swapped in an old R7 1700 chip in, using a $10 Quadro card for initial setup and ran it headless (eventually, I got a $25 Mini PCIe VGA card and $20 M.2 Key E to Mini PCIe adapter, although I haven’t actually had to use the monitor output since initial setup).
I don’t know if things have gotten better, but Raven Ridge sort of sucked w/ Linux last year anyway. Even with the latest kernels at the time (4.18 or so?) I was getting occasional lockups unless I disabled all C-States. I didn’t have issues w/ the R7 1700.