This is my first public repro and my first selfmade clean webpack 4 starter setup, too. I am going to use this as a starting point for future projects.
node: v8.9.1, npm: 6.1.0, webpack 4.12.0 I do also use a content.json and twig-files with a main template.
It's recommended that you use Node Version Manager to install and manage Node versions.
$ nvm install && nvm use
$ npm install
Starting development-server:
$ npm run dev
Building a dist folder:
$ npm run build