1: Yes, I have seen some of @AtaxyaNetwork Proxmox posts. I'll go back and read them again.
2: No big deal, I only have like 5 vm's on Proxmox, V2V is my choice of tools!
The Xen / XCP-ng equivalent for VMXNET are Xen PV device drivers which either come from Citrix Xenserver, XCP-ng or the Xenserver project itself. Check the Wiki. It describes the installation pretty well: https://xcp-ng.org/docs/guests.html#windows
As for 3D acceleration within the VM there is hardly a comparable option unless you do some PCIe pass through of a GPU.
According to Microsoft you need to use their built in backup feature or a software that supports AD and VSS which will tell the VM OS that it is going to be backed up.
Unless you do this there might be corruption of the AD Databases according to Microsoft.
ALL THO we've been backing up our AD servers with XOA snapshots (Both normal backup and incremental) and had only 1 issue since we started using XOA in 2016.
Since that issue we also use a guest agent (From Ahsay CBS) that makes a Windows System State backup and Windows System Backup.