Chainging the keys is sufficient to have CloudReco work with your own Database, however, you will not see any augmentation in your 3D view (using the CloudReco sample) if you don't associate some metadata to the image targets that you have uploaded;
those metadata must contain one of the following strings:
For instance, suppose you have uploaded 2 images to your Cloud database, you could associate a metadata containing the string "samplebook1.json" to the first image target, then a metadata containing the string "samplebook2.json" to your second image.
Concerning the Book.java file, You need to keep Book.java and BookOverlayView.java only in case you want to achieve the same kind of visual effect as in the sample, i.e. if your application also needs to display book covers as an augmentation on top of targets,
otherwise, if you plan to have differnet type of augmentation (such as a 3D model, like the Image Targets teapot for instance) then you can remove those classes, of course.