With the advances in gaming on Linux in recent years, it is so tempting to switch full time. I would absolutely love to, but I am a Game Pass Ultimate subscriber and it is where I play a lot of my games on PC. I know you can use the cloud version, but I cannot stomach streaming games in their current state, so it is a no go. A large portion of my Steam library is compatible, but anytime I have done an install I end up giving in and going back to Windows for games.
I have an Index and it was seamless for me. Everything runs fine in Proton, and I didn’t have any performance issues with my 2070 super. Tried the same games in Windows and it was the same experience, plus a couple of FPS (I assume because it wasn’t going through DXVK). Can’t speak to your other questions, though–those are outside of my experience.