Thanks. I think I understand everything except why do you keep the shipping box if you buy 1 copy or remove it if you buy 2? If you remove it with one copy, does it delete your payment info you're trying to save?
Any time you buy 2+ PS4 games, they are automatically shipped in a box. If you buy one copy, they ship it in a mailer unless you add a box to your order (which I recommend doing). If you buy 1 PS4 and 1 Vita copy in the same order, I also believe that you will not get a box UNLESS you buy 2 PS4 and 1 Vita. Basically, you need to have 2 PS4 copies of any game/games to get them shipped in a box. Someone from limitedrungames can probably clarify this better.
I use the item in my cart to make sure the info is saved. All my single copies I buy I always add a box, so by doing this in advance it makes checkout much easier. Hope this helps.