We have almost 38000 members here and we are 12 mods which is not too many. In case one is absent another mod can do the job. If we were less, the threads couldn't be moderated in time and the attachments couldn't be approved in time too. For making a board run smoothly, you need people managing forums. I know a three big watch communities/forums with above 150000 members and they have over 30 mods each.
See, now thew board I mod at, we don't check approve it before it goes up, the members post, and then if it needs to be tweeked, we do it after the fact. We also have access to the admin board...the owner just wants **** done, and doesn't care who does it, because we all have been there from the beginning, and came there from a board that closed...so the 5 of us, have worked together for about 5 or 6 years. It works in our situation.