@gregeporter - as Sam has mentioned, there is not a great amount of developer documentation at the moment that describes the structure of the internal components.
Back in 2017 this same question was posed elsewhere on the forum, and Xav Riley shared a diagram giving a rough breakdown of the major components. (It is still fairly accurate, except for the bit which enabled MIDI communication (osmid) - this was replaced not too long ago):
I see you also found the developer documentation on the wiki.
Those pages and the above diagram are not totally up to date, so there may be some slightly inaccurate information here and there. I too am interested in trying to update the developer documentation, and have started this process, though it is not always easy to find the time to complete it 
If you have more specific questions, I’m sure someone would be able to help 