My Kindle never saw any WiFi connected to it. Everything goes through Calibre. I only read dead authors, so I don’t feel bad about pirating my books.
Sometimes I go buy used books at my local bookshops just because you should support your local bookshop.
Yes but not necessarily in the way you think. “Bad” posture is usually linked to weak muscles and lack of mobility/flexibility. If you strengthen/stretch your muscles and connective tissues, eventually it should help correct your posture.