Hi,
There are many presentations under the architecture track from the most recent Cocuhbase Connect conference: http://connect15.couchbase.com/sessions/
Please click on the architecture track. Your questions above are answered in the presentations.
You are correct that the documentation focuses on how to use Couchbase and N1QL, rather than under the hood. Lmk if the presentations work for you, or we can answer specific questions on this forum.
Gerald