1. I usually do the updates in the evening when turning off my laptop. I click “update all” (or so) and then choose “shut down” in the selection that appears at the bottom. Then I can leave the laptop and it will automatically reboot to install the updates and then shut down completely.
2. Yes, that number of updates is normal
3. I don’t know of a way to (un)select specific “system”-packages within Discover
4. The updates are usually fine. I can’t think of any case where a routine update caused trouble for me. I prefer getting the security updates (and other improvements) quickly. Just once, I intentionally delayed the updates for a few days before an important deadline, where I needed my computer to work and wouldn’t have had the time to deal with issues

Why is this downvoted?