For gamepad support: in case it's useful, here's a commit on github from when I added gamepad support to a Game Boy js emulator (used it here on itch.io). Firefox support for standard mapping may have improved since then.
https://github.com/chrismaltby/gb-studio/pull/305/commits/bffdeef5ce1930031850a39fe1579aa610b281b3
The graphics look great, and the palette switches are a nice touch. Love the sound too. Nice work!