In my case, I currently use a Macbook Air M1 (my personal one which I currently don't need as a laptop). Absolute overkill and in some aspects annoying - only two USB-C ports for example - but it was available and it's fanless and doesn't need much power.
When there's a MacOS security update and the Macbook reboots, do NAS functions work before a local user has logged in?
I think I turned auto update off on this machine but if it reboots, you would have to login first. Doesn't bother me, though. I don't have any uptime requirements.
Any launch daemon service will load and/or start at boot, only user-domain services require a login (like the Dock or menu bar would)