No amount of planning and preparation is going to make your community explode into life.
Even if you pulled off the most successful marketing campaign ever, persuaded all the top people to join, had the greatest content of all time, the community still wouldn't explode into life.
This is because communities don't explode into life. The biggest of pops is still just a pop. A surge of activity fades. Momentum dissipates. Then you're left with an empty shell, a lot of disappointment, and some explaining to do.
Communities grow steadily. They rise from their slumber. A few members join, then a few more arrive. Members participate, then keep participating.
This post is as true for communities as it is for books.
Planning for a big launch is a bad idea. It makes far more sense to plan out the first 3 months. Create a big calendar of what you're going to do. Be specific. Figure out who you're going to approach, when you're going to approach them, what's you're going to tell them, what activities you're going to initiate in the community, what discussions you're going to initiate in the community etc...
These questions are more important than a big launch. It's the organizations that put together a big plan for the launch and a small plan for post-launch that struggle the most.