re: unattended setup.
You're both right - Apple's official zero-touch setup requires MDM + DEP, which needs Apple Business Manager (and yes, a DUNS number).
But for VMs specifically, DEP doesn't work anyway - VMs don't have real serial numbers that can be enrolled in Device Enrollment Program.
VNC-based setup automation is the only practical option - it's what the ecosystem has converged on for macOS VMs. Lume connects to the VM's VNC server and programmatically tabs, clicks, types through Setup Assistant.
I wish the virtualization framework would allow you to simulate your own MDM stuff. Would be very useful for integration testing MDM implementations themselves...