i ran proxmox with passthru for any vm i wanted to use it on. i had a 2ndary older gpu for main access, and used fluxbox with firefox for the initial setup which i would start x on if i needed graphical interface, i had multi monitors, with multi inputs, so i could switch input after loading vm. This meant i had access to proxmox as headless, or with GUI, There is a software kvm that can be used for swapping mouse/keyboard functionality. After boot once the vm side of things was sorted i could simply qm up ### of vm after logging into cli of headless proxmox. In terms of deciding which OS will boot you can do this via the vm settings option"start on boot", which can be turned on and off whenever, but this would require you know beforehand which os you want next if you plan on shutting down your pc. I basically left mine on, but this isnt always feasible. docker is fine headless and ssh into from your windows/debian instance... there are many other container image options in proxmox. For secure DL of windoze iso that doesnt require you already be running windows to access the download section to obtain an iso i used this from inside proxmos ( not technically the best way, but it is what i chose to do - a better way would be via your linux vm, then upload from that via the browser based access to proxmox. hope that helps :)