I really like BuddyPress for interactive communities, so I tend to go overkill and use it for anything that might possibly evolve to need its functionality in the future. Combine it with an events plugin like Buddyvents or EventPress to create a much richer user experience than you’d have with just an events plugin alone.
The other upshoot of using BuddyPress is you can implement group-based forums really easily out of the box, which may ease other parts of your development process.