While it may look simplistic, I had to overcome a few hurdles in my own c64 knowledge, a good experience
For ppl that want to know all the techy details:
I programmed it in C with a mix of inline-assembly here and there (using the cc65 compiler)
The most challenging part was the polyphonic music. I ported the example from the c64 reference manual from BASIC into c-code, deciphered the encoding mechanism, encoded a few extra fields for repeating sections of melody, and there you have it
For the PETSCII art, I made use of the Kaleidoscope V4 tool, saved out my art, then wrote some loader code with inline assembly.