One set will do all the cars in the set and the add-ons. You don't use one on the Baggage car forward since it won't couple to the Kato or MTL coupler and you only use two on the articulated cars. So when I finished the set and one two car set add-on I have enough left if I order another two car articulated chair car. Oh yeah, you don't need on on the rear of the observation car. It wouldn't look right.
