1. Yes, but if it goes under 20%, the performance may slow so the recommended range is 20% to 80%. Over 80% can be fine as well.
2. Some streaming services may tell you to pick what genres you may like as your setting up your account, however most others will use analytics (e.g. your browser history or what shows you have watched before)
3. I don't understand what this conclusion part means, but I am assuming it means a 2nd part to question 2. The conclusion I have come up with is that streaming services would like you to watch more shows, meaning more watch time, meaning more money for whatever streaming service it is to pay their workers (at a HQ) and then more shows, and the cycle repeats.