Not sure I understand the question.
"how hard would be be to get beyond most of the fluff and set it up for mostly dedicated use as a Kindle reader?"
There's no set up. You press the kindle app icon on the home screen, log in to your Amazon/Kindle account, and that's it. It's been a while since I fired up my Fire, so you might have to sign into Amazon to boot it, which skips a step, you just press the Kindle Icon.
I would say if all you want is to use the Kindle App and books in Amazon's ecosystem, and you are willing to forgo the paper/eInk look of a paperwhite, then it's probably the easiest device to do it with.
FWIW, I agree that the eInk is easier on the eyes, but I got tired of dragging around an extra device several years ago, and do all my reading on my tablet, and it's fine. The only annoying bit is that you can't buy things in the Kindle app for Android (or Apple) anymore because of some Play store terms BS, so I have to go to my Amazon App, buy a new book, then back to Kindle to read it, but the Fire Tablet should sidestep that.