i prefer a less cluttered interface, but can understand that it would be confusing for a first time user, perhaps you can do an "intro" the first time the app is opened. I have seen this being more popular recently. There are several screens that shows basic functionality. Some people will still skip it of course, but then they can refer to the manual. If the flashcard module isnt purchased, will the "+" still show up? If not, then maybe when the flashcard option is bought there can be a short tutorial as well.