Yes, there's several diagrams in the new HAF documentation to show data flow and algorithms.

I would guestimate we have at least six devs who have a lot of experience with hived (and other sibling chains such as BitShares, Peerplays, EOS, and BEOS), and we have several other devs who are gaining familiarity with the code base.

Probably a similar number who've worked on hivemind, which isn't technically core code, but is responsible for a lot of the social media behavior of the blockchain.