a lot, it's actually not that difficult to remember stuff from the books! my way to do so is to: 1. consume a book 2. read a couple of summaries 3. write my own summary (yabc.bdut.ch) as simple as that!
100%. i also like to write something short about my understanding of the topic and the book before reading :)
I write summaries + use Readwise to make flashcards that I review (mostly) every day on quotes I found particularly memorable/important/profound.