I've returned and my new approach was to learn:

1. The repl for exploration 2. The language (read nix.dev) 3. Read the nixos manual

And with that it started to make sense.

I've actually gone the other way - not everything is meant to be run. If it's not in the nix repos, I'll try the fhs, and if that doesn't work - well I probably don't care enough to beg it to run. For me the fact that my base installation can never break is not negotiable.

I definitely didn't learn much of nix(os|pkgs). I never bothered learning about flakes. I just have a configuration.nix and a user config.nix, and a "fhs" default.nix and that's it.