3. I think (not positive) you can be signed into Kindle on as many devices as you want--what is restricted is the individual books, which will have their own DRM limits. For instance, back in the day I had some textbooks on Kindle and found that some had DRM that only allowed me to have them on 2 devices. Other books I never ran into a DRM limit with, but also never needed or tried to have them on more than 3 or 4 devices.