For your last point, you don't have to use the channels (which will anyway be deprecated at some point iirc), and you can pin the nixpkgs version in your nix fi

For your last point, you don't have to use the channels (which will anyway be deprecated at some point iirc), and you can pin the nixpkgs version in your nix files (like it is done in https://garbas.si/2015/reproducible-development-environments.html https://garbas.si/2015/reproducible-development-environments...)