Just offer a paid forum where members post for you and you can hire staff. Start some contests and special offers and you would get a lot of members and earn good with the forum.
SMF is a good platform in secure aspect. The most important thing you have to think first is how much money and time you can devote to the work. Total Marketing depends on the money you are spending. Strategies will be build as per the money you are spending. And of course time is essential. More the time you give better is for development and as well as for the marketing of your forum.
Have you looked and using Mybb instead of SMF? I like it more than SMF personally http://www.mybboard.net/
I suggest you to start firstly a website in the respective niche and after you will have got enough traffic transform it slowly in a forum.