Sounds like a decent choice. I'm not familiar with Kindles or Fires, but do they let you download from the Play store or just Amazon's App store? Android and Apple devices are much more useful than the black/white kindles if you plan to use it in medical school, especially due to the app stores. I use my Samsung Galaxy Note 8 for reading PDF textbooks (and you need color for some of the diagrams, histology, etc.), to pull up medical calculators, to quickly google info, to take UWorld exams and to connect to the hospital's EMR system via Citrix. Others have Netter's Anatomy installed. I doubt the black/white kindles are capable of that. This might be premature though if you're not yet in med school as they will probably come up with much nicer devices in a few years.
The Galaxy Note has a minor benefit in that it has a Wacom digitizer, which allows you to get more accurate handwriting vs. the nubby stylus used for other devices. Granted, it's still not very good at taking handwritten notes compared to paper and pen. For studying, reading PDFs tend to be very responsive, but paper is still more comfortable. It's great, however, when you need to search keywords.