I only have 3 installs of NixOS already, two for work (a server and laptop), and a third for a personal use (desktop). I largely started out by copying a public config from the community. Now I just copy a few kilobytes between the three from time to time via git repo to keep all my kernels, kernel modules, patches, net config, package versions, and system users/groups permissions in sync via lock files. And my user dot files too, but you don't need nix for that last one.

If I have to do something multiple times, like copying a distro across even a few systems more than once, then I figured I'd just revision control it via lockfiles like any other software project.

That all said, NixOS is a hell of a rabbit hole; great for lazy admins and hobby tinkering alike:

https://xkcd.com/1319/

The top graph reflects my stable work install for robot software development,
but the bottom graph is my personal install for hobbies and home lab.