The way I see it you have two problems that are not related to the number of people that MAY show up. First you have two long meats to cook, I would drop the brisket because of the food cost and add chicken, it is cheaper for the customer and you make more per serving plus if you cook too much you won't have a lot of lost profit. Moinks take a lot of prep time and you can't really get enough to justify the time. Ribs are ok since you can cook them ahead and finish at the event. Since this is a two day event you will have some idea before you cook for Saturday. Be really careful or you will be buried.