What are you trying to document? What kind of documentary are you trying to put together - professional - personal - hobby etc..
Also note that any documentary using video is going to need editing (you'll need software for that as well as a good computer -- you might also need other gear if you go for the casset type video cameras )
You'll also have to consider sound and lighting as well in your setup.
You need to give more info - you might also get a slightly better response from a video forum - since the dominant theme here is stills photography (we do have some video users of course, but not the same community input and info that you might get from a dedicated forum)