Well written analysis on this. I'm in the exact same position and considered Samsung DeX, but it's not at the level I want it to be.
I have the Raspberry Pi 4 (8GB) and it's my first one. I bought it to learn Linux and eventually move away from Windows due to privacy concerns. On top of that, I want my Pi to be a media server (via Plex) as well.
As for the OS, have you considered using Manjaro? I found this video so I can take full advantage of the 64-bit OS and it's running pretty well:
I'd like to know your thoughts.