Hi,
although you said amazon to be a B2C ecommerce and everybody knows it from that perspective but the fact is, amazon is also B2B and C2C. It has sellers API, affiliates and marketplace.
When we start making project plan for such platform we not only think about technology but also think about Big data handling, concurrency control and durability of platform on simultaneous user's transaction.
Thus, we will make system arcitecture first along with security and cloud based server implementation. As you have good budget so, if interested talk to us and finalize the project.
Regards,
Mit-