I'm getting the Nikon D5100. What particular things can I do to achieve the film look?

I know things like setting it to 24p and lowering contrast. What else can i do? What's a good and cheap external mic. And what kind of flash?

What you want to do has to be done in post.

Here is a video shot using the Nikon D7000 and I have no reason to believe that you can't achieve similar results with the D5100 since it has the same sensor.

Getting the motion picture look has a lot to do with how you light your scenes. The motion picture "film grain" look is done in post