Most comments prior have mentioned all that needs to be said for quality of game. That said I understand that you're still learning. Keep it up and keep working at it~!
As for the CC0, yes you don't have to credit any creator or artwork/music licensed under CC0. I will say though it is common courtesy to credit art/music even when licensed under CC0 out of respect and some people even send a small message to the artist just to let them know.
Cheers!
P.S. just tagging @troisnyx