NixOS docs themselves are a tad lax, but it will get better.
Learning nix itself is also important:
Just this morning I was having issues with a wacky dual-boot install with NixOS and Windows sharing an EFI partition, and quite interestingly ChatGPT and I were able to troubleshoot the process and get it resolved in under half and hour. I was really impressed by the specific configurations it was giving me for my /etc/nixos/configuration.nix , so that is also another resource you may consider leaning on when you run into walls in other documentation sources.
GPL is the only good license out there. MIT just leaves too many opportunities for abuse because corporations won't ever do what is in the best interest of humanity.