Which key is the saddest?

If you're into that, check out Adam Neely's channel. There's been a few videos on that and related topics: ▶ this video (Spoiler: lots of historical context about tuning systems, but also raising the issue of timbre of specific instruments)

I recommend checking out Adam Neely's channel, where he touches on some similar concepts: ▶ this video link link

Re #2, I'm not a programmer, but as a writer I find the same thing to be true. I work better with a pen and legal pad than a keyboard. I've got this feeling that we have neural pathways built for typing and, subconsciously, we favor phrases, words, and sentences that are easy to type. I know I even have a tic where if I pause to think I'll insert extraneous commas. It's kind of like how musicians tend to improvise around licks and scales that they have practiced a lot. There's something to thinking about the idea of a song on paper that is more creative than unintentionally falling back on chords/forms that are easy to play. (Adam Neely discusses this very well here: ▶ this video )