At 1:11 in this video they cut to a slo-mo scene of the two main characters. N Sync - Gone - YouTube
If I want to replicate this in editing, I suppose I'll have to shoot at 30fps just to make sure I have enough frames to get a smooth slo-mo correct?
What other settings should I be aware of in order to get myself the best possible file for edit?

I'm editing in iMovie.
Thanks for your help.

Andy,
You need to do some more research on slomo. You'll need to shoot at lease at 60fps to achieve good slomo. If you're on a mkII that means you are out of luck :) There are software programs that fake it, but it's always best to achieve it in cam. Can you describe what you're trying to do? Just slomo or is there slomo lip synch involved?

Yes, 720P @ 60 is nice to have and produces smooth slow-mo video for long takes.The cut to slow-motion at 1:11 is a very short clip and could easily be replicated by shooting at normal fps with the 5D and then slowing down the frame rate in post.