Our system already takes care of all that in its own way, so what you described may be trying to reinvent the wheel.
First, bear in mind E-junkie is not a payment processor, so we do not handle any actual payment funds at any point. Buyers would pay directly into your chosen payment processor account, such as PayPal. In order to use our shopping cart and other features, you would need to have an account with at least one or more of the independent payment services we support:
Once you set up your products in E-junkie Seller Admin, we provide you with ready-made HTML codes for your cart buttons. You would simply copy the codes from us and paste them into the HTML source of your own Web site pages, wherever you want our buttons to appear among your own layout, text and images. Buyers would simply click an Add to Cart button for each item they want to order from you. You also have the option of using Buy Now buttons that bypass our shopping cart and take the buyer directly to instant checkout for just one item at a time.
If you enable Shipping/Buyer's Address in the product's settings, that will trigger automatic collection of the buyer's shipping address during checkout and, if you're using Cart buttons, optional calculation of shipping charges in the shopping cart before checkout.
Our system is designed to be really quite straightforward to configure and set up, and you have a fully-functional 7-day free trial period which begins as soon as you register for an E-junkie login. Our Getting Started help page is a good place to begin setting up your E-junkie service: