Hi Peter,
Great to hear that and W3.CSS is not one I've used before so I'm intrigued to see the results.
The best reference I can provide is the example projects such as this one which uses Freemarker templates:
https://github.com/jbake-org/jbake-example-project-freemarker although feel free to pick any of the other example projects depending on your preference for template engines. The example project represent an example integration with a CSS framework, but are not meant to be the only way you can integrate. I just took a Bootstrap template page and converted it to use JBake templates.
Unfortunately there is not a guide at present, primarily because the end goal is always different for each person.
Do keep me up to date with your progress.
Thanks,
Jon