Let's say you are already rolling with a forum (in terms of self-generated content) during launch. How many users do you expect to sign up before people actually start discussing?
I've been in plenty of new forums with only a few users and everyone gets talking right away. Better when more users arrive but you don't need many at all.
In fact many people start faking 3 or 4 user account, posting and replying themselves and shortly afer new user begin to sign and chatting. Of course you need good categories and threads selection. ·
Set up the right categories and start talking !! It is important to start talking alot at the beginning!
It's not about how many users. You can have 5000 users and still have a forum where no one talks. Then again you could have only 5 and they could chat all the time. It's about how enticing you make your forum to make them want to use it. So making a forum that looks like many people are already talking is the way to go about it and eventually people will be talking all the time without you having to help it along.
i've had 70 users regsitered these past 10 days and no one has started talking, but me (i talk to myself every day)