Have you considered simply pointing your users to the relevant parts of what currently is https://nix.dev and pick them up when they are done? Basic concepts and workflows are outlined in the beginner tutorial series. The most important aspects are the Nix language, the various Nixpkgs mechanisms for constructing derivations to build software, and the module system.
You could even support the documentation team with improving the material to the point where it puts your audience in a place where you need them to continue teaching them what you actually wanted to teach them.
You may correctly object that this would be quite the detour. I worked on improving Nix documentation as my day job for a couple of years: there’s no royal road to Nix, as all the “it’s complicated” answers indicate. For more specific discussion of flakes or not, see: Discussion of flakes, from 2025 NixOS Community Survey Report