> I also have the feeling that the tutorials start with the details, instead of starting with an overview

Yes. Reading the official docs, or Nix pills, gives exactly this impression.

I've read some good documentation away from the official docs on how to start using the package manager.

But understanding the overview of how to package things yourself is all wood and no trees.

There's so many moving parts in nix that knowing how they all interact, and which ones are important for your task at hand, is a headache.