My configuration.nix before I gave up on using NixOS. May go back to it some day.

configuration.nix

# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  boot.loader.grub.enable = true;
  boot.loader.grub.version = 2;
  boot.loader.grub.device = "/dev/sda"; # or "nodev" for efi only
  networking.hostName = "riddler"; # Define your hostname.
  time.timeZone = "America/Chicago";

  # $ nix search wget
  environment.systemPackages = with pkgs; [
     wget vim tmux git unzip kate sutils killall
     firefox
     openssh autossh
     elinks
     docker
     tetex pandoc texlive.combined.scheme-basic texlive.combined.scheme-small
     jdk
     gcc gnumake
     service-wrapper
     python36
        python36Packages.numpy
        python36Packages.pandas
        python36Packages.scipy
        python36Packages.jupyter
        python36Packages.matplotlib
        python36Packages.scikitlearn
        python36Packages.scikitimage
     sbt-with-scala-native
  ];

  # Some programs need SUID wrappers, can be configured further or are
  # started in user sessions.
  # programs.mtr.enable = true;
  # programs.gnupg.agent = { enable = true; enableSSHSupport = true; };

  # List services that you want to enable:
  services.openssh.enable = true;
  virtualisation.docker.enable = true;

  # Open ports in the firewall.
  # networking.firewall.allowedTCPPorts = [ ... ];
  # networking.firewall.allowedUDPPorts = [ ... ];
  # Or disable the firewall altogether.
  # networking.firewall.enable = false;

  # Enable CUPS to print documents.
  # services.printing.enable = true;

  # Enable sound.
  sound.enable = true;
  hardware.pulseaudio.enable = true;

  # Enable the X11 windowing system.
  services.xserver.enable = true;
  services.xserver.layout = "us";
  services.xserver.xkbOptions = "eurosign:e";

  # Enable touchpad support.
  services.xserver.libinput.enable = true;

  # Enable the KDE Desktop Environment.
  services.xserver.displayManager.sddm.enable = true;
  services.xserver.desktopManager.plasma5.enable = true;

  # Define a group
  users.groups.docker = {};

  # Define a user account. Don't forget to set a password with ‘passwd’.
  users.users.jcchurch = {
    isNormalUser = true;
    home = "/home/jcchurch";
    description = "James Church";
    extraGroups = [ "wheel" "networkmanager" "docker" ];
    uid = 1000;
  };

  # This value determines the NixOS release with which your system is to be
  # compatible, in order to avoid breaking some software such as database
  # servers. You should change this only after NixOS release notes say you
  # should.
  system.stateVersion = "18.09"; # Did you read the comment?

}