8.3. The demo doesn't do ... (pick one)

That is because it is a demo. It is not intended to be a finished catalog, just a starting point.

That being said, you should think long and hard before abandoning the checkout schema. Years of experience have led to the production of the userdb, transactions, and orderline tables, and the structure of the checkout page. Any changes to the data structure should be thoroughly tested before deployment, as obscure errors can cause major problems in order logging.