Yes, clients would have to edit in the manager. And I believe you can set up the user to only see one "Context", which is where their site is. So that would solve the "overwhelm problem", maybe.
Oh, I just thought of a way to limit the person to 4 documents, maybe. You could give the user 4 blank documents, and then mark each document as editable by that particular web user. But I’m still not sure if they could still add more documents. Maybe if they log in as that user, they can only see those?
User management is a part of a system that I find highly boring and irritating to deal with, so I do it as little as I can.

So maybe someone who actually knows about Revo user management will chime in.
There has been feedback about Revo that the user permission system is tricky to understand. I believe that most people are in agreement on that, and it should improve soon. Evo’s user permission scheme is not overly easy, either.