The stuff behind the scenes, such as the database, is simple and flexible, so I don't have to consider that. So this is all about what the users need, and that means what he needs in the GUI (it's a web application).
I know this is a very wide question. I could ask it much more specifically, but I think there has to be people out there, used to attack such problems, that have very general guidelines.
It could be great, if you have some resources for learning more, whatever your answer is.