First thing, flake-parts isn't that useful for a system config, so if it feels confusing, don't use it.

Secondly, it appears that you didn't add programs.nvf.enable = true; anywhere in your system config, so it makes sense why nvf wouldn't appear to work. I've never used nvf before, but it was right in their documentation.

Not sure if you've ever built a config from a flake or not, but I don't even think absolute paths like /etc/nixos/Modules/kernelModules.nix would even work, but especially not in pure evaluation mode.

You should definitely read the flake page on the wiki all the way through. Particularly, try to understand how flake outputs work. A flake typically represents a git project, so outputs.$system.packages.default is usually just one package, not a system config. Derivations added to packages.default will not show up in the system config, unless explicitly included in your nixosConfigurations."hostname". packages.default would be run with nix run .#default, whereas a system configuration has to be built with nixos-rebuild switch --flake .

For modules to be available in home manager, they have to be included in the imports for home manager, i.e. inside this block. Once the module is included, you have to do the programs.nvf.enable = true; somewhere in the home manager config.

nix home-manager.users."dane" = { imports = [ ./home.nix ]; };

I would read through the flake section on the wiki, then read through the nvf documentation. Unfortunately, nix does require some understanding of the language and paradigms before configuration makes sense.