First of all: Do you need reproductibility? I.e. having the exact same system on multiple machines? If not NixOS might be a lot more complex than what you need.
Secondly: Instability does not mean what you think it means. People read instability and think the system will break, when instability actually means your system will be updated. In the context of a server, an update can be destructive, for day-to-day users it’s very rarely so.
Finally: why Arch or Nix, why not Ubuntu, Mint, Pop or any of the other dozens of distros that are usually recommended for new users?