Docker provides a working and sufficiently complete TeX installation which is used on Travis to build the most recent books (e..g the booklets with the blue cover plus a couple other ones). But the build itself relies on makefiles, templates etc. Pillar is only one step in that process.
Currently I'd advise checking the books from��
https://github.com/SquareBracketAssociates that have recent changes and a successful build on Travis, and checking their build process. The build process has evolved this last spring, so it might differ from books that were not updated recently.
Other than that Stef and I are probably the most able to mentor someone about Pillar, unfortunately we're currently both on holidays for a couple of weeks.