Do we have to make the game art and music? Can we just reference online sources?

Well since there’s  unfortunately like 10 composers available for every game made I think you should go for original stuff :) If you cant find someone here post a request on reddit gamedevclassifieds!

Hi there! You're welcome to use existing assets, or create your own.

E.g. Piskel for creating sprites, and Bfxr for creating sounds.

I really like how Piskel turned into an opensource project and how its interface is cool, i've not yet tryed Bfxr thanx for the link

concretely i still use The Gimp in pixel mode

it's not a problem if i use music ( I haven't a midi piano, it's really hard to play with computer key :) )