How to make a short professional documentary? Where to start?

I would like to make some short documentaries about homelessness, street children… Etc, so far I installed Sony vegas pro, I also bought a professional camera Nikon, what other techniques I need?

You must start with planning. Detailed planning.

Script
Storyboard => Defined list of shots required
Locations
Actors/Speakers
Cameraman
Sound man
List of Shots per location
Estimated time in each location
Transport to/from location
Security for camera and personnel
Catering