This looks great! I'm no designer, so I always appreciate seeing other folks' ideas on how to design things. To shout out some other inspiration, there have been a few Calibre redesign projects.
In particular, Kemie Guaida[1]'s redesign posted to Reddit has been a major design inspiration (and she deserves credit on the repo, which I will address shortly): https://old.reddit.com/r/Calibre/comments/udzumn/testing_a_n...
You're able to see the entire overview of the project here: https://www.figma.com/file/g4ntqXWa6C0PRGrG3WjyXM/Calibre-pr...