As others have said, by the time you get the car, the paint is fully cured so you can do what you want. There shouldn't be any contamination under the plastic but check anyway, if there is, then go ahead and decontaminate, and polish. Again, I doubt seriously you'll need those steps. Also, there shouldn't be any oxidation and any scratches will be from washing or rubbing the wrap off instead stretching it off. You shouldn't need more than a good wash and then use whatever wax/sealant you decide. I have two cars, one, a driver I work out of and another, both bought new that have never needed any polishing and are pretty near cobweb - not just scratch or mar - free. They are four and three years old.
Doing a weekly car wash using good methods, not a lot of touching the paint does more to preserve a cars appearance than just about anything. I make a living polishing cars but mine have never needed it.
