Seconded on Cockpit project w File Sharing.
Probably not best practice, but it’s possible to install it on the PVE host itself since its ZFS manager and Identity manager plugins and other features fills some gaps in what Proxmox doesn’t do (or would have to drop to CLI to do).
Also recommend RClone in a systemd can take care of various file movements, syncs and backup tasks you may need against the host, vdumps or SMB file shares.
Seems reasonably decent gear. You didn’t mention, but first try the free stuff? It might be a case that you need to update BIOS and other firmware and software (radeon boost)?
After update to latest bios, you could also try a 2nd DDR4 to run dual channel and see if that helps. Hopefully your existing stick is max clock speed for the processor.
Otherwise, yep probably option 1!