I have several servers I’ve acquired over the years setup in a proxmox cluster

You have found the smallest, tiniest, itty bittiest potatoe to get upset about here. You could run this on a toaster.

If this is what you consider a resource monster you’re gonna have a really, really rough time

Deity of choice willing, never lol

Yeah UFW is the way to go, but when you run into an embedded Linux device that only runs iptables and can only be accessed via ssh?

Well…. Keep that drink handy

iptables!