I have decided some time ago that it makes little sense to open a forum unless you make it some targeted, extremely specialized community that is not already in existance.
There are too many forums already and of those only the well established ones continue on.
I get so many invitations to post in/moderate forums that I end up never getting around to any of it.
I wish you all the luck, but getting a forum started is quite difficult. The only way to success I can see anymore is if a number of well established sites with good traffic all share a forum. And that is being done quite a bit also.