I have a mod from about a year ago called "FAB - Forum Activity Boost" which is posted here on KWWH.

It was something which I released in Beta and then kept the full version for myself it works so well.

It add's realistic fake replies to topics and really makes it look like you have a community. It works too as it encourages others to post. Now I know your going for the real approach and would advise you to explore that fully first. I'm just letting you know it's there as a backup.