Pretty much all my VMs are headless Debian for whatever purpose I'm using them. I've tried Ubuntu but it has done some weird shit with snaps over the years, things like installing Docker concurrently as a snap when I've already had it on as an apt package then shitting itself unpredictably until I figured out what was going on.

If you can, use LXCs where appropriate to reduce overhead usage. An LXC container will use much less resources than a full VM. You can even set up Docker on a Debian LXC and I'll set up a few hosts like that to partition my applications.

There's little reason to install a desktop environment for a server. Learn how to set up SSH keys and use the command line, most server applications don't have GUI interfaces anyway unless they provide a webpage for admin, in which case you don't need a DE anyway.

If you do need remote access with a GUI, try installing a Guacamole webtop instance to remote into, and manage your services from that.

If you're setting up Proxmox either use the Proxmox ISO or start with Debian Bookworm. The only Linux machines I have with a GUI are my desktop and my laptop, both running Debian with KDE. All my servers run Debian unless there's a good reason not to.

I run Debian on all my vms, they have no GUI installed at all. I manage all of them over SSH

1. Debian, unless I'm doing something specific like Home Assistant OS
2. Yeah, usually. The GUI uses so much system resources just to sit there and be unused. That said I do have a Windows VM for Quicken that I remote into to manage my families finances. Of course that isn't headless.

You mentioned selfhosting, so it's safe to assume you want to install servers. Servers are headless by default.

But the proxmox admin web interface also makes it easy to access a VM's GUI remotely.

Do you actually need a VM for your use case? You might use docker containers or LXC instead.

Normally I use VMs for situations where a container isn't available (Windows, openwrt) or the VM is better supported (arguably home assistant).

b) Should it be headless?

As most people have said, typically a server is headless as it has less overhead. But it's going to depend on your use-case and needs. If you have the spare ram/cpu/disk and want to put a GUI on every VM you can. In my case, most of my VMs are headless with a couple that have a GUI out of necessity.

a) What Linux OS do i take? Ubuntu Server?

Typically folks either pick what they like best or pick what's recommended by the service they're trying to run. (Remember, typically you run one service per VM, so everything about the VM can be tailored to that service. That's pretty much the whole point of virtualization -- so that you don't have to get multiple services cooperating on the same machine.)

My default go-to would be Debian, but again, it's really a matter of personal preference.

b) Should it be headless?

GUIs take up disk space, RAM and CPU cycles, so it's more efficient not to have them (especially when you're virtualizing and therefore running separate copies per VM). However, this is 2023, not 1993, so it's not that big a deal.

would there be any advantages of installing an OS with a GUI?

The advantage would be that you could administer the VM and the service inside it using a GUI, if you're into that sort of thing.

In general, most services are designed to be administered over SSH or via a web interface, so a GUI shouldn't be necessary. Also, in general you ought to be scripting the administration of your VMs themselves using e.g. Ansible, so a GUI shouldn't be necessary for that, either.

Lots of good advice here. Something I did was make a base Debian VM that has common tasks already done- my network configs, docker installed (but not enabled), the guest agent installed, ssh root password login (until I'm done setting it up). When I want to try something, I clone the base vm, change the IP, enable docker if it needs it. Set up my new services, copy ssh id, disable ssh password.

Try to stick to the same disto and you give KSM a better chance of reducing memory usage.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

4 acronyms in this thread; the most compressed thread commented on today has 15 acronyms.

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Usually it’s handy to have a display during initial setup and cfg. Also, with x windows port forwarding … you access your server gui over a network like god intended :)