@pitaj Thank you for that, it's actually very helpful (I'm a complete newbie to nodebb so even the most basic pointer has value to me).
I have done some work around what I want to achieve, and I think it's going to be best achieved by separate auth (oauth2/oidc) provider (keycloak) which will allow users to authenticate and access both the xmpp and nodebb. I can keep nodebb mostly vanilla, and perhaps look at notification (and maybe pub/sub) to xmpp.
That way it leaves things pretty much as they come out of the box (experience teaches me this is easier for maintenance and updates), with functionality linked on a basic level, but with people able to access the same member list on any services.
This is the simple, clear, direct help I need. "Chats are stored in the database (duh) and are sent in and out through socket.io".