The second insert is set to use the Name, ID and price hidden form elements, do these actually have a value when the form is submitted, you can double check by viewing the source of the confirm page before submitting it.
Instead of using the Dreamweaver Insert Record behaviors to store the order information, you will get better results using the eCart store order summary and store order details behaviors.
in eCart 5, you can use the checkout wizard to create the checkout pages and simplify the process of setting up the order management. It will also handle the storing the customer number in the orders table for you.
In asp the code to destroy a session is:
<% Session.Abandon(); %>
add that after the </html> tag in the checkout success page.