Instead of turning the whole website into a paid forum, what about adding a private section that is membership based. John Stone from
John Stone Fitness - Welcome! does that. The private forum allows people to share private information and talk about private stuff that they don't want to be indexed by google or viewable by others.
If I remember, at johnstonefitness, the private forum membership was $20/year, and there was also a plan to get more features if you paid more. I did that myself for one year about two years ago. Both the public and the private forums were pretty active, although naturally, the public forums had a lot more activity than the private forum. However, the private forum was very neat because people were talking about things and posting pictures that they would not do on a public forum. I myself became a private forum member after having participated in the public forum for a little bit when I saw the value of the participation on the forum.
I like that idea applied to this forum because it allows the thousands of people who come here to get some very valuable help in their personal development, but who wouldn't pay $20 for a forum subscription. It also allows those people who would love to be much more open and talk about a lot more private details to do so without being concerned about non-forum members viewing it and the info being googled. If the numbers of those wishing to have the private forum are high enough, perhaps it can allow the hiring of a forum admin and the addition of those other modules.