1) You advertise what is offered on Amazon and mark it up - YES

2) You get paid, and order it on Amazon directly using the Send as Gift which eliminates the invoice and gives you the ability to White Label the message as if its from your store - YES

3) But before you go to Amazon you use your affiliate ID to get even a more lower price - YES (however make sure the affiliate ID has a different contact info versus your billing information otherwise it would conflict with amazon TOS)

4) Order is fulfilled and you get paid on the customer end and affiliate end? YES