That kind of depends on what all the Fixin's are, the makeup of the crowd, Women, Men some Kids and if there is any other Protein, Burgers, Dogs, Etc. If you go Meat plus 3 sides, women and kids will be good with 2 Bones, 3 Bones for men. Dinner Rolls are a good filler as well. If Meat plus 2 sides and no other Protein you are talking 3-4 Bones per person or 3 serving per Rack. Feeding 150 people you are talking 50 Racks. You need some serious equipment to pull that off! A large Smoker or a smoker plus Grills for reheating will be needed. Additionally is this a " Feed them all at once " type of think or a dealer promotion that food will be available to employees and customers throughout the day? With a single seating, set your timing so the Ribs are ready no more than 5 hours before service. This lets you get all the ribs cooked and resting wrapped in foil and piled on each other in coolers to stay hot. If this is an all day event your best bet is to get all the ribs cooked, wrapped and Chilled to less than 40°F and in coolers with Ice. You can then reheat in the Smoker or on Grills set to Medium heat and serve as needed. Go with only Rub and have sauce on the side, less chance of Burning during the reheat. Since you are feeding a crowd you need to keep Sanitation and Safety in mind. Cold sides need to be on Ice and <40°F and Hot Sides and Meat in Chafing Dishes and kept above 140°F. Lots to think about...JJ