Another adult fiction site encouraged participation in the forums by putting its password inside the forum, so readers are forced to enter the forums to get the password, at least. But I don't think you guys would want to do that.
About the author interaction: That adult fiction site's forum actually has a pretty active author-reader conversation threads! Especially for well-known authors and long-running stories. One of the good points on that forum. I don't know how they do it, though, because the nature of author-reader relationship there seemed stronger, although they don't have review posting features. Maybe it's just because that site's older, so they have more longtime members.