1. Install NixOS as usual, set up user shell with git.
2. Clone this repo to ~/dotfiles, cd into it, rename username.
3. Optionally create a machine specific file root/etc/nixos/machines/<name>.nix.
4. stow the config files to home-manager and root dirs:

stow home
sudo stow root -t /

Edit /etc/nixos/configuration.nix as usual and only import ./machines/<name>.nix:

{ config, pkgs, ... }:

{
  imports = [ 
    ./machines/thinkpad.nix
  ];
}

...or just add machine specific configuration there:

{ config, pkgs, ... }:

{
  imports = [ 
    ./common.nix
  ];
  boot.initrd.kernelModules = [ "i915" ];
  services.xserver.videoDrivers = [ "modesetting" ];
}

5. Run nixos-rebuild switch and home-manager switch.

The "filesystem files" are symlinks to their equivalents in ~/dotfiles, you can edit either. When adding some file, run stow -R home/ or sudo stow -R root/ -t /.