I'm not the best person to answer your questions, but here are some starters:
- While there's at least one Python interpreter for web browsers (named Brython), the PyGame API is another story entirely. You'll have to rewrite your game for the various HTML5 APIs instead. As that can take time, maybe look at a framework like Phaser first?
- Unless you have a license to the music, either implicit (free culture) or granted by the rights holder, using it in your own game is copyright infringement, regardless of price. But that's your problem; to the best of my knowledge, itch.io doesn't police its members in that regard.
- There are some submission quality guidelines you'll want to review before uploading your game, but they're easy to meet and likewise not heavily enforced. Mostly it's just common sense stuff to get your game noticed at all (let alone well-received). Don't worry too much about it.
Hope this helps!