All of that said, I think the Apple iOS allows developers to block streaming of downloaded content Vs internet content.
The advantage of android is that you can just screen mirror and show whatevers on your device.
You may find a cheap android tablet is a good investment in this regard, but by all means give it a whirl with what you have.
Chromecast works for Netflix and YouTube... no reason why Amazon would be any different
Isnt Chromecast like Amazon firestick? Just a device for streaming content via an unlimited internet connection ? I cant see where the download and stored for play later features?
Yes, but, given Chromecast is made by Google, it allows more freedom with Android devices than the fire stick does. Egg. Screen mirroring as above.
Neither firestick or Chromecast have any ability to download, store and then playback content.