Hi all!
Thought this might be interesting or helpful to some of you.
I created a Ghost Starter Theme that’s available on GitHub. It’s meant to provide some boilerplate to jump start the creation of a custom theme.
It uses Rollup and PostCSS to process JavaScript and CSS files. There are also scripts to start a livereload server and another to zip assets to facilitate uploading the theme to your site.
I wrote up a brief piece describing how it works, too.