There are two basic approaches to BEHIND THE SCENES/MAKING OF videos.
The INTERVIEW version, where cast and crew are formally interviewed in a somewhat staged fashion. You will still need a video guy (at least, if not more than one and sound) to shoot BEHIND THE SCENES footage to use as "B-Roll", which is the footage you put over top of the interview so you can make seamless cuts. You can also use still pics as B-Roll in either case.
There's also the FLY ON THE WALL approach, which is to tell the story almost entirely from the B-Roll and shoot interviews as the film is being shot and staying somewhat unobtrusive.
Great examples of this type of thing can be seen on the 2 different LORD OF THE RINGS dvd sets. On the incredible 4 DVD sets (12 total), the first approach is used. The cast & crew were interviewed after the shoot and regaled the viewer with their tales, and extensive use of photos and B-Roll made it all visually interesting. 2 years later, they released the 2 disc versions where the 2nd discs were documentaries by Costas Botes, each one 90 minutes for each movie where it was almost exclusively B-Roll with only a few interviews, all done on set during the shoot.
I combined both theories and did interview segments, but also long B-Roll Fly-On-The-Wall segments for IN THE TRENCHES OF AN INDIE FILM (
http://amzn.com/B001PIHP0E) and you can see a sample of the Interview style here:
https://www.youtube.com/watch?v=OIehEnqdV6M