Hi Boris,
The documentation available at this stage is what is available on Beans official website.
Regarding the structure of the framework, it is explained in this article. I would sugget to open Beans Core files and get your head around how things load which will make it much easier for you to understand how do modify it. About the markup names, you can dynamically find them in your browser inspector, this reply will help you to understand how to do so 🙂
It is not on the roadmap to build a Visual Builder.
Happy coding,
Thankyou 🙂