1. I assume that latest **stable** (e.g. 19.03) ISO will be used for installation.
2. Check `services.xserver.videoDrivers` in `desktop.nix`. If you not sure it's better to remove the line completely.
3. Default network configuration is VPN-only, so if you don't have plans to use it you need to change iptables rules (remove `iptables -P OUTPUT DROP` from `networking.nix`) and remove `services.openvpn.servers.vpn` from `networking.nix`.
4. GUI settings is optimized for 3840x2160 on 15".