This post gives some great statistics on Chinese character frequency, but I'm curious about the total number of distinct characters that appear in a "typical" book. By "typical" I mean something like a popular modern novel: say, "The Three-Body Problem," or the translation of the first Harry Potter.
I'm guessing the number will be disturbingly high, much greater than 3000, which I think I've heard quoted as a good benchmark for reading fluently. If, as suggested in the first link, the top 3000 characters cover at most 99.4% of characters that appear in random text, that's depressingly low. It means if you know 3000 characters, then on every page (I just counted around 1000 characters/page in Harry Potter) there's a rough average of six characters you need to either look up or accept not knowing how to pronounce!