I'm a first time director making a low budget horror/thriller movie in Costa Rica "Gringo Loco" and I've been telling my cast that they will receive a percentage of the net profit, if it turns a profit, but I have no idea what a fair percentage is. None of the actors are very experienced. The camera operator and the AD have a little experience. I'm doing everything else, including the lead role.
I'm not counting on making anything, but I still need to write contracts for everyone, just in case we get lucky. I think it mite make a little if done well.

What would be a fair percentage for the cast(5 supporting actors, 2 one scene actors, probably 10 lines each, and 5 extras)?

What is a fair percentage for the camera operator?

What is a fair percentage for the AD?

Thanks a lot for your thoughts!
Jeff