This might be ambitious, but I think Hazbin should try to corporate as many different styles of music as possible for the soundtrack and individual character songs. Musical theater, pop, rock and roll, heavy metal, jazz, techno, orchestral, country, rap, K-pop etc.
They definitely should! Especially considering how many people live in hell and how they’re all from different time periods with different tastes in music. Like each character can have their own music that’s representative of their personality or time period. Like Broadway for Charlie, jazz for Alastor, swing for Angel and his family, ragtime for Rosie or Baxter, 50s rock and roll for Niffty, etc. It’d be really interesting to see for sure!