While I agree that the process could stand to be less convoluted, if you preorder you do get all of the bonuses. When you preorder you are given 2 codes: the Heavensward code (which won't be available to you until the 23rd), and the early access code. The early access code has to be redeemed on https://preorder.na.finalfantasyxiv.com/na

Once you enter the code there, you will be emailed a new code, that you enter on Mogstation to gain access to the preorder items.