Chronoforms Modification - Paypal Checkout Process

We would like to pay a developer to create a multi-step checkout form that can submit payments to PayPal using the Website Payments Pro API. This extension will be reused many times in many different scenarios. It must be developed so we can just install it and be ready to go – with default form fields already in place. Think of a multi-step form as a shopping cart with a pre-loaded product. When the user completes the first transaction, another product becomes available for purchase. Upon clicking that product, the product is purchased without the user having to re-enter any information. Our hiring criteria: We are looking for programmers who are highly experienced in programming Joomla Extensions and interacting with PayPal’s Website Payments Pro’s API in PHP. To get an Interview: Please provide portfolio of PayPal Projects AND Joomla Extension Programming. We'd like to see source code, not just a link to a website. Detailed specifications are attached.