Originally Posted by Ryan S~
No narration needed but believe me you want a professional to narrate if you're going to do the film circuit with it. It's worth the money.
Agreed. And I think if you ask some local audio post houses, they may be able to recommend some narration guys.
Ryan's way of shooting a doc, I think, the most economic way of shooting one. Write out everything you want to know, get the questions prepared well in advance, GET your answers (or at least find an interesting alternative), and shoot a lot of B-roll while you're on location.
I know guys that just went out and shot stuff, and did this for years before finally being able to put something together. They eventually put something together, but unless there's a purpose behind it (ie: documenting the life of a tree, from seed to saw)... it's usually best, in my opinion, to approach it as if you were approaching any other film: script it, schedule it, and shoot it. Stick to your deadlines.
As for crew, I think it completely depends on your subject matter and what tone you're trying to create. Personally, I'd hire a professional sound guy, and will spend money on a cinematographer depending on what camera we're using (and how much money we've got!)
But that's my take. I'm sure you'll meet some people who have had very different experiences, and have made it work in completely different ways. That's one of the things I love about working in film.