They are decommisioned datacenter drives, this could be for a variety of reasons (including errors). There are many discussions online about them wiping smart data.

It depends on your use case, I have a few of their drives in a nas specifically for media. I received one bad drive that failed my burn in tests, which they exchange without issue. All of my important files are stored on a seporate ssd based store.

All depends on your risk tolerence and needs.

Serverpartdeals is good. https://www.goharddrive.com/ is another option. Generally slightly more expensive than serverpartdeals, but with better warranty. Both are reputable options

Have you considered making your own firewall running opnsense? You could toss in a 10g nic or two

Maybe you’d be interested in https://wazuh.com/

Proxmox has a virtual monitor in its web interface, so you can access the desktop of a virtual machine that way. It’s a little clunky but works ok for quick configuration. Alternately you could remote desktop into the virtual machine.

Quicksync is a little more tricky. GPU pass through is a pain, and I’m not sure off the top of my head about that. You can Google “proxmox quicksync passthrough” and see if any solutions will work for you. There’s a chance that all you would need to do is set the processor type correctly in the virtual machine settings, but I’m not sure.

Have you considered replacing the OS with proxmox and running everything in virtual machines?