We need a :trump-straw: emote a la 
nasezero
Gonna be pretty funny when the release is delayed and the military doesn't adjust the days off for the suckers who re-enlisted.
Ah yeah, you can enable a desktop environment on the Proxmox machine and (I assume, haven't tried it myself) have an experience more or less like regular Debian with VMs running in the background (that you can shut down to free up resources when gaming). I would consider this really over-engineered, and only worth doing if you're happy to get the learning experience and dealing with the added complexity, and possibly tearing it all down and starting over if it doesn't perform well. Absolutely nothing wrong with just running Ubuntu/Bazzite/whatever natively, and running docker containers on that can be spun down when gaming.
I mean I guess you could run Proxmox on a VM in Ubuntu, but I'm not aware of any use cases for such a setup (it's fine for trying it out, I guess). Proxmox is more intended to be the platform which you manage VMs on top of.
What I'm suggesting is installing Proxmox as the root OS on your machines (at least any that would run Linux anyways), join them together into a cluster, and then install VMs on top of that. To be clear, the VMs would still run on individual machines, but Proxmox gives you a handy web UI from which you can mange any machine and any VM on those machines. You can also later explore LXC's, docker swarm, and kubernetes, but I think just starting out with a simple Proxmox cluster running a couple of VMs is a good place to start. (And then backup said VMs using Proxmox Backup Server)
I have one of those houses near me, and it also has an "I stand with Ukraine" sign next to it 
No, but Portainer can be used to help manage multiple VMs within a Proxmox cluster. You'd set up Portainer on a VM like you would any other system, and then deploy an agent to other VMs (or even other machines on your network). Think of Proxmox as your hardware abstraction layer, and tools like Portainer (or dockge, dockhand, etc) as further abstractions for your containers.
And what makes it hard if a machine is already a standalone ubuntu machine???
I would have to wipe the Ubuntu boot drive and replace it with the Proxmox iso, and then re-set up anything I have running on Ubuntu within the new environment. It's mostly just tedious migrations that I don't want to do badly enough right now, lol.
Are you planning to expose services to the internet, or are you keeping everything only locally-accessible? If the former, you'll definitely want either: a reverse proxy handling SSL certs between your router and any exposed services; or a vpn tunnel like wireguard.
I'd also recommend giving Proxmox a try. I was a little intimidated when I first started setting up my own cluster, but it's honestly not that hard and I wish I had done it before I set up some of machines as standalone ubuntu and debian. Even with 1-2 machines I'd recommend it for the convenience of being able to manage VMs on every machine within a single web UI, as well as making backups much easier especially with Proxmox backup server. Note that the default installation has some subscription nag and defaults to an Enterprise repository for system updates, but there's this post-install script that takes care of all of that.
For off-site backups at friends' houses, you could set up S3 storage on a device they plug into their network, although this would require its own dedicate reverse proxy and cert management + said friend letting you into their router's settings page. You could also offer to host your own and "trade" space, using the argument that even if they're not interested in self-hosting it's still a good idea for everyone to have some off-site backup space that isn't at the whims of Google.
A gif of a little guy doing construction work
Unlimited
on br*tish "journalists" 


We're ruled by fucking dorks. Dweebs, even.

DLC
This argument should only be applied to cars