Thanks Tim and Pierre. Indeed because of all the links to the images and videos fooling around with the categories will make a bloody mess. To be safe I wil just leave it for now as it is and just check in which copies I used the same questions and do some double editing.
Next year I want to upgrade to 2.x and that will be the moment to clean up and reorganise.
Seeing in the future: if I move all the questions to a sitelevel category along with the uprrade procedure, will I still have to edit questions by hand if they are in copy of a course in which attempts have already been made? In other words if I change a question in the sitelevel category which is used in say three courses will the questions change everywhere?