The fact that your server would be locally on site eases two of the major pain points... If the Windows games you're playing on your VM are resource intensive, why not instead just do a V2P to a bare metal gaming rig each time you want to refresh the OS from your "reproducible" image? This would eliminate many more difficult scenarios... however if the games you're playing on the VM are not resource-intensive, especially if they're 2D, then sure GPU passthrough stuff may be the easiest and best-performing option for you considering all the overhead of maintaining a separate, physical box.

Use a Type I hypervisor and expect to tweak your configuration endlessly... and once it's working, endlessly still more...

I'd recommend ProxMox... here's a setup that worked for somebody: https://forum.proxmox.com/threads/gpu-passthrough-tutorial-r...

I've set up an online gaming company/system that's rather novel but my implementation is far removed from yours, as you have dedicated graphics on a local hypervisor.