GPU passthrough; display over network or display port/HDMI?

[Northbadger]

I aim to self-host a windows desktop to be accessible in/away from home as VM on a single proxmox node.
I have twin Nvidia quadro K2200 cards installed in separate IOMMU groups.
These GPU are quite old now and I expect to upgrade them as work requires (initially light CAD/FEA) but not immediately if this is not a hard-constraint to enable setup.
I'm happy to give only the windows VM GPU access, or share among future VM.

So far I have attempted the following:

1. to blacklist Nvidia drivers in proxmox,
2. to instantiate a windows VM with relevant virtIO drivers,
3. to add respective PCI devices to the VM with all functions selected (incorrect settings maybe?)
4. installed the latest Nvidia drivers to both GPU within the VM.

The proxmox node boots and is visible on connected display through to a screen showing a flashing underbar. When I start the VM, said screen goes dark (browser access remains). I suspect there is a way to get the monitor to subsequently show the VM output over DP/HDMI. Is this a red herring? I could always setup a RPi / other thin client with monitor, keyboard & mouse and thus always connect over network with GPU outputs unused.

Have I failed one or more steps and how might I test this?
Should I reconsider my approach?

I'm a novice so any advice would be much appreciated, cheers.
Apologies if this information is covered well elsewhere.