I use a Fire HD8 tablet for browsing the forum. Works well for that. I would guess it works fine for reading e-books, but I don’t use mine for reading e-books so can’t really compare and contrast the two.
Id get the e reader so that you can concentrate on reading. It would be annoying to me to be reading and be getting Facebook notifications or soemthing. I like to do one thing at a time
I have had a Fire tablet. It was ok and served its purpose. Slower than my old iPad I inherited. But I really wanted something with a bigger screen to use. Battery life was just so so. The kindle’s App Store was also lacking a lot of options I found out that I wanted. I couldn’t get certain apps that are available on iOS or Android App Store, for example.
I’ve never owned a kindle e reader so I can’t compare the 2. The idea of a separate device if it’ll help you use it more is definitely something to consider I think (like the wise @POET said).
I also want to remind you about the Amazon Prime days coming up. So I think if you can wait, it’d be worth it to get a deal on July 16-17 like @Moonbeam said. Very smart advice to think of that!!
I hope you get the perfect fit for you! Enjoy it! I read audiobooks. That’s the only format I can handle since sz. I’m so grateful for audiobooks!!