The shotgun mic will help with most of that, depending on how far away the subject is from the camera. You can also try to find a variation of that mic with a longer shotgun (the longer the shotgun, the more the sound will be isolated to what you're pointing it at). But I think that mic will be just fine. The good thing about that setup is that it's simple and it all goes straight into the camera. You won't want to fuss with recording audio to a separate unit and having to sync it up.
The reviews for that mic are really good though, so if it were me, I'd feel totally comfortable buying that mic. Whatever camera you get, make sure it has a 3.5mm minijack input for a mic (it most likely will; the camera that I linked to does).
iMovie will work just fine.