Self-Hosted Main

I would just run Ubuntu, setup docker and use kasm workspaces to do what you wanted

Not really. You could buy a kvm so you could remotely connect to that device and then select the OS you want in grub. But that is essentially connecting a monitor and keyboard.

From your Linux systems you could run grub-set-default or grub-reboot. I don't know if there's a version for Windows.

Does your server use a server motherboard? Or are you reusing a desktop style motherboard as a server?

A lot of server motherboards support IPMI which allows access over the network to change BIOS / UEFI settings and install the OS remotely and stuff like that.

Use efibootmgr to rearrange the boot order and then reboot.

If you are using Grub for booting, your could do a script for editing the default OS and use that for rebooting.

Or alternatively use networking capabilities of Grub as shown in this exemple.

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 :)