I've never experienced 2, 2a, or 2b.
3: This is a Zoom problem, I believe. I find that Zoom periodically enables the microphone even though I'm not in a meeting, and you can see this in the latest macOS by looking for the orange dot in the upper right corner of the screen. The workaround is to quit Zoom, or go into Zoom's settings and change the microphone device to your Mac's.
6: You may have hit a hardware problem with early models. Happened to me, and I also often experienced a screaming feedback tone when I put the earbuds in my ears. Apple will replace them for free.
4, 5, 7: Definitely.