I'm not really friend with Unity so i may not be of help in that. But i can share some more websites where to grab art for games. Perhaps some other gamedev can share more.
Open game art. Good webpage to get free art resources for your games (3d models, sprites, textures, music)
Also here in itch.io you can find an asset store with both free and pay resources.
Extra music.
Some tools to create music without knowing sh*** about musical theory.
https://splice.com/sounds/beatmaker
https://musiclab.chromeexperiments.com/Song-Maker/
(i made a copy paste i did in another thread haha.)
I'd like recommend you check the ToS and License for the art and tools you use.
Since you are still learning Unity. Didn't you tried with GODOT? It's similar (more or less) to Unity and more lightweight.
Good luck. If you need any help or have any doubt don't be afraid to ask.
:-)