Despite how good some forums are, not many people join forums from personal sites. The biggest forums are usually forums that are involved on sites that people use to get help with something (like this forum is part of a site that helps with Flash, etc).
I can only assume that traffic was low to your forum because your site was not up yet, so not much traffic there and people didn’t know what your site was about.
So perhaps your idea of getting your site up and running and building up traffic before relaunching is a good idea.
