1. A text editor, mated with some templates for the various types of notes I take. It's simple and fits my needs.
2. Regularly.
3. I don't have anything you can describe as a setup. I use those text files, a calendar, and that's about it.
4. I have a weekly task file. For the next day, I add what I need to do the night before.
5. About 20% (?).
if your primary OS is linux then this makes sense.
It is, but I've used that with macOS ChromeOS too.
what do you do if you've to draw something that might not come in a text file
I don't draw, whether with analog or digital tools. OK, I sometimes do but in a paper notebook. But that's very rare and what I draw is usually crude, ugly, and simple, and transitory.