Great idea! There's a rule of thumb for creating communities around a forum such as this, but basically you have to assume that only 1-2% of people will actually post to it. The irony being that if few people post, there's little content and little push for future users to post as well. It starts to look like a an inactive forum and people just take what they like or is relevant and leave.
Offering incentives is a good idea, but with your kind of site the aim should be to drive as much traffic as possible. This benefits your affiliate network and advertisers, but mainly it means that you have a bigger actual number of people in the 1-2% that are going to post actively.
There's a few opportunities around that you could leverage at the moment. Drop me a line
morgwn@digitalartscience.com.au and we can work on some campaigns or traffic driving exercises.
Morgwn