I would park the additional domains for now.

Start building content on your new forum and blogs first. Once you have some content on the sites, try to find some other forums and blogs related to your market and start participating. This will allow you to start building some credibility while also getting some ideas for more content on your site.

See if there are any online directories that are related to your site and try to get listed. DOn't pay to get listed with spam type directories or link exchanges, but if something looks legitimate, try to get listed.

Have you done your keyword research? Use a free tool such as Keyword Discovery or the keyword tool within Google AdWords to see how many people are searching for your keywords.

Since this is a very focused market, make sure you know where people interested in this subject gather. Go to those places and create a presence for yourself.

If all elese fails, or if this is taking too long, try doing some pay per click advertising. Make sure you have some stat reporting tools on your site so you know where your traffic is coming from and what they are doing on your site. Keep an eye on your stats and keep tweaking your site until you start to get more people exploring the site and signing up.

Good luck!

I'd make it top priority to get your site at the top of organic keyword listings. Do this by building 5 to 15 new backlinks per week.

By content building on the forum do you mean starting new threads, even if others aren't contributing to the discussion?

I always wondered what's a good rule of thumb for starting a forum, as in, how much traffic should you have at your already established site/blog before opening up a forum?

You could also do some pr and put it on article sites, ping your blog to keep it updated but i also agree with organic keywords.

Do you mean writing a stand alone article and then mentioning your blog in the bio? I don't think that most directories allow for advertising within the article itself. So you have to be strategic and write about a related topic, and keep the adver in the bio.

Article writing and submission can still be a valuable way to build links and traffic, but it isn't like it was a couple of years ago. If you want to try article marketing, visit ezinearticles.comhttp://www.ezinearticles.com and try submitting a few articles with your link in the bottom bio section. Take your time and write a good article. People need to read the entire article if they are to make it to the bottom bio section and be interested enough to want more of your knowledge and writing.

I think forums are a great way to get moral support and get open to the issues that people are thinking about. Well, IMO of running forums, no one will come and just start posting, add content and exclusive content would be great, it gives members something to talk and think about.

Do some banner advertising on other forums, participate in them and let the members know about your forum putting your forum and blog links in your signature. Participating in Social bookmarking and networking sites is also a good way to get visitors. Other than this, there are many more ways that you can find going thru the forum.

one of the most important thing to gain members, make interesting topic, and give them enough reason on why to join your forums, a unique and interesting content will do.

Forums are easy way to get support and get open comment to the issues that people are thinking about. To gain members need to make interesting topic, advertising make them understand why to join your forums and attractive, interesting content will work I think.