We are having a fairly personal reception with around fifty people and would like to have a potluck dinner to cut costs. Me and my FIance would bring the main courses but how do I delegate who to bring what without being rude? It is okay for me to send cards to those whom RSVP explaining we are having a potluck and give them a few options on what to bring so we dont end up with 5 bowls of potato salad?