Nothing is overkill if it helps. The only danger I see is that you can spend so much time getting the wiki just right that you never actually write the movie.

I haven’t used it in years, but I remember loving VoodooPad for the Mac, which makes for a fast and nimble single-user wiki.

We’re using an industrial-strength MediaWiki for the bible on a very complicated project that involves a number of specialists. It’s been a good way to keep people on the same page over the 15+ months we’ve been in development and production.