It is possible that you cannot include all the tasks on your list in your goal statement. That is ok, because you should focus on one main use case, which is how most people will use your application. Awesome apps do one thing well.
How will people use your app?
By now, you've identified your main use case, target users, and key features. Your main scenario should also consider the user environment in which your app is used. For example, a young mom with her baby at daycare might use your app to note a nice stroller (potential multi-tasking, pausing and continuing the task later). A different user might plan her next laptop purchase at home, in an armchair, without interruptions.
Concentrate on a few key features
Look at your task list again. Filter your list through the goal statement. If the tasks do not align with your goal statement, exclude them in your app.
Describe each core task as a feature and then ask yourself, is this feature essential? Or is it nice-to-have but not required by the target user to complete the defined task? Be honest with yourself. If you end up with a short list of features, you are on the right track.
Remember, the best apps usually do one thing well. Apps often fail not because they have too little features, but too many.
Your app in its most basic form
Once you have a few key moments, you can translate those steps into screens. You can sketch out the user flow, that is, how do your users go from one screen to another to complete a task.
Think about the information a user wants to see and record. Consider which user interface (UI) elements correspond to the information above. Put things that your users need most often in the most prominent places in the screens. Even just writing out the sequence of moments helps define a wireframe model of your app and its features.