Help with planning project

I’m planning a project I’m doing for a client which is a fresh sushi bar. What I’m doing is a sushi online service! Customers should be able to register, log in and then pick their orders. Besides choosing dishes from the menu, the major purpose is to order customised plates (which will be very visual with a plate and drag and drop gfx).

I’m considering different approaches to acheiving this. The security is not an issue as the payment will be done cash on delivery and not online. The service will not have heavy traffic.

What I have in mind is not a design like a e-commerce shopping cart system, but rather a step-by-step interface.
Step 1: “Welcome! How many people are you?” input number of ppl-> X
Step 2: “Order #X Compose your own plate or pick from menu?” Compose: goto step 3, Menu: goto step 4. Repeat this X times, for each order.

And so on…! I think this will be much easier to do. Furthermore the order does not have to be stored (in a database or otherwise). It just needs to be sent with e-mail to the sushi bar.

My questions: I have very little experience with PHP and mySQL so I would rather do this with XML (to store user information and retreiving prices) if it’s possible. How would this work? Is it ok to store the order in a variable inside flash before e-mailing it, or does it need to be written to a database? I’m worried about what happens if more than one user is using the service at the same time.

Please help me!