Many small stories are better than few long ones. If you write long ones they should have identifiable small pieces. That way you will be able to construct verifiable milestones for your delivery schedule.
Screen prototypes may help you formulate your ideas and communicate with your customer, but they are not sufficient. You need prose too.
You could begin looking for a use case template (see link on course home page) that suits your needs.
Back to the cs681 home page.