Getting the download server behavior setup to work with your scenario should not be too difficult but it will depend what you would like the user experience to be. So if you can please describe how you would like this to work and I can help you get it going. The tutorial is for a specific scenario that may not be the best fit for you, so if you describe what you need it to do and how it should work that would help me to get you started.
As for the order id this should be using the eCart session id binding. What is the binding that you are displaying on the pages?