Launching a community is a bad idea.
It's not the community, it's the concept of a launch. It focuses efforts on the platform. It focuses on the short term. It delays important activity.
The major moment in the birth of a community is not when you launch a platform. There are many steps to take before you do this (preparing the organization, establishing objectives and audience analysis amongst them).
The major decision is when you begin engaging with potential members.
Focus on the day you begin interacting with members. This puts the focus beyond the platform, established a long-term mindset (you will continue engaging for a while) and encourages you to do the important work (interacting with members) right away.