The first thing you would need to worry about is getting the forums active. That isnβt going to be easy by any means. When they all have an active member base and getting a constant stream of traffic that is when you can start making good money from them.
Google adsense is one idea. Depending on how popular the forums are and how many you are going to develop, you should easily be able to pull in $xxx a month to start off with.
Most affiliate networks donβt usually accept forums. I have run into this problem before and it is rather annoying. You might find that you can make more money selling banner ad spots directly do webmasters and businessβ.
Another easy way to make money is by selling text links. On the homepage and / or sidewide. Depending on how much traffic you are getting and your PR, this is another sure fire way to make an extra buck.
Home that helps.