I'm currently learning about vagrant (and docker) and try to find a way that best fits my needs for moodle plugin development. This way I've found your thread. Thank you for sharing your work with the community!
I wanted to comment/suggest just a few things. As I understand it what you have build is a Vagrant Project and not a Vagrant Box, isn't it? (see https://www.vagrantup.com/docs/boxes.html). I thinking about creating a Moodle Vagrant Box. This would bring the advantage of easily setting up additional instances when needed for different projects.
It may be more comfortable to not have the Moodle code included in the repository as a zip file but clone the Moodle repository on provisioning. And when the moodle directory would be a vagrant synced folder it would be easy to use an IDE or editor on the host machine for development.