Unfortunately I can’t do this justice in a single response. The short answer is that we’re detailing the MUSTs now in the normative draft of the specification at GitHub - solid/specification: Solid Technical Reports. One thing that’s worthwhile to point out is that we’re in the process of portioning out the core client/server protocol (Solid Protocol). The purpose is to allow a more flexible evolution of ecosystems between clients, over a more consistent and well-defined interface.
Hope that helps. If you’ve got questions on specific MUSTs or MAYs I’m happy to chime in on those.