Alright so I am editing in 24p advance in final cut pro and I want to do a bit of slow mo. I've heard filming at 60i is best but I don't think I can mix 24pa and 60i footage. So my question is what is the best file setting, and could I shoot at 30p and mix it with 24pa?
What version of FCP are you using. You shouldn't have a problem putting a 60i clip on a 24p timeline regardless.
If you have doubt, give it a try and see what happens. Experiment.