For reading I would have a place with plenty of light, natural and artificial. Maybe a whole wall is a large window, and one wall would be a bookcase with tons of books covering a lot of topics and some classic literature for inspiration. Lots of comfy throw blankets and a few cozy chairs, maybe one large couch that reclines with phone chargers built in. A sound system with a record player and a cd player and a radio for audio inspiration. Lots of old movie posters or literary posters on the remaining walls. Cross between cozy coffee shop and old library.
For writing, maybe something a little less cozy, a desk for the computer and printer, good source of internet for research and a coffee maker. Again, a good sound system, I like to write to music. Inspiring quotes or posters on the wall, but less comfy furniture. Maybe a small bookcase with writing and reference books within easy reach.
I kind of like the idea of a converted shed, office in the back yard. I read somewhere that is how J.D Salinger wrote Cather in the Rye, to free him from distractions from the house. He would go to work there, and people knew to leave him alone. I love the idea of an ADU just for writing. Like a mother in law apartment with a small kitchenette and bathroom. Keep work and home separate in a way. I would like that. And a beautiful garden outside it for more inspiration.
The Infamous Jennisfora Strikes Again...or something like that 