Adubya

I’d say Arch Linux if you are sure about doing something else than Proxmox. The wiki and help posted on the internet might benefit Arch switch currently. You can get the experience you are looking for and it doesn’t box you out of using Nix. Arch will get you going sooner IMO.

NixOS seems fun though and I’ve only recently starting messing with it. You will do best engaging with what you prefer best. The NixOS switch could pay better dividends in the future though.

If I recall this hasn’t been the first time NixOS has had to consider Palmer/Anduril. You could keep an eye out for the auxolotl project that is doing an alternative/fork of Nix.