Backend, Checkout and PayPal Integration for jCart

Hi guys! There is this tiny AJAX shopping cart called jCart ([login to view URL]) out there. I really like it since it is very clean, lightweight and easy to implement into any website. In my opinion it is ideal if you only plan on selling a limited number of products. However jCart lacks features such as a little back-end and a checkout and order creation process. I envision a very simple and basic back-end. It should be capable of managing categories (no subcategories), products (category, sort order, name, description, price, stock level), orders (order id, order password customer email, shipping address, billing address, list of products ordered, customer comment, payment method, payment status, shipping method, shipping status), payment methods (PayPal Integration only for now), shipping methods (domestic, international) and shipping destinations (select able by country). Customer account shall not be created; all the information will be stored in each individual order. The current checkout page needs to be expanded accordingly. PayPal should be the only payment channel (for now) and should become fully integrated (PayPal IPN to confirm payments and change payment status of the order). Notifications should be send out to a specifiable E-Mail address when an order was created and when a payment was made. An order confirmation should also be send out to the customer after a purchase was made. The order should receive a random id 12 figure ID (upper and lower case letters as well numbers) and a order randomly generated password. The customer should be able to click on a link such as [login to view URL][12-figure order ID] and be able after entering the order password to get information about the order status. The code should be written in PHP and in a similar fashion that jCart is written in. Nice and clean, this is what I would like to go for. As I was thinking of only offering a couple of different products and since it is meant to be used with smaller sites, to use XML as a storage engine. I don't know if this is feasible, so please let me know what you think about that. The HTML design of the back-end or checkout are not important, either leave it really simple or tell me what you are thinking of. Maybe we can figure something out together. This is what I loosely envision. I am of course open to any suggestions on how to improve the whole thing. Please contact me if you need any additional information.