5. Make sure you cover all topics on your boards but don't create too many topics. Don't go over 20-25 different topics.

I hope you are talking about the main subjects you discuss, not the threads themlseves, since you need HUNDREDS of threads to make people want to join.

When I launch a new board I open 20-30 threads DAILY, or even more

As for the title: How to start a successful forum, you cannot start a succesful forum, you make it so All starting forums are empty and not appealing, but with effort we can make them successful Anyway .. great idea for the topic indeed.