I think they are different issues "Technology" and "Business Model". Now you want to create an application which using J2EE technology. The most important thing you should do is design the system with high level detail. And then design the database scheme and make sure it can fit everything u need for the application. Same as other application, you need to deisgn those things first. J2EE is just a technology which help you to build a better and more scalabe application.
I would recommend you a book "Enterprise JavaBeans" from O'Reilly. Thats a very book ! and also you can go to http://java.sun.com/j2ee
. I am sure you will find something very useful.