Can I sell several products on one order form?

Yes. You can create one form per product, or add multiple products to the same form. With multiple products, the visitor picks the one they want on the second page of the form, where the products are shown as a selectable list. One form for all products means less to maintain than one form per product.

The products always show as a selectable list, not a dropdown. You can reorder the products in the form, for example to put your premium product at the top or the bottom.