my opinion is that if any kind of sealant is applied, even to brand new paint, the car should be gone over with a finishing polish first. a dealer who applies sealant, is probably not going to do a great job of polishing/decontaminating the paint, and just put sealant over dirt and imperfections. ----(think of how long some cars sit on lots. or how many times you've seen them stacked on transporters going down the highway. they are never perfect when they arrive at the dealer)
if you are not wanting to invest in a dual action polishing system (porter cable, griots, rupes, etc etc) and do all of this work yourself on the car when you get it (preferably without the dealer even so much as washing the paint beforehand), i would say you should find a professional detailer, and use the money that you would have paid for the dealer's paint sealant option to have a complete new car detail done for you. --you will be much happier with the results.
once that is done, just get some good mild car wash (plenty of options on autogeek that don't strip sealant/wax/coatings), a couple grit guards and some buckets and you will make that initial detail last for a long time with proper washing and sealing/waxing.