YAY
hmmm...
while it would be cooler to add original instruments, it's fine.
hmmmm...
maybe have the voices actually be voices, but the audio gets crispier from the astronaut as the songs move forward. Also everyone forgets about the background track in songs.
there are three tracks.
1. the opponent.
2. the player
3. the stage without either.
this allows for instruments without having characters play them.
this is also why having original songs helps, it allows the song to play better off of them.
if you feel like having the song be close to canon, and could possibly fit in with the final game lore, know that boyfriend is named boyfriend, is dumb, and has social anxiety so that's why he sings.
imagine the first song being who wants to knaw on human bones
Of course, this is only if you want to. I'm just telling you things that could make it better fit. Some characters sing words, but it wouldn't be boyfriend.
It would be cool though if you explained how they got to space, especially considering the non-family friendly lore that got the game it's name.
and also, on normal mode, if the song goes a little fast in some parts, have the arrows be less. and in hard mode, GO WILD.
hard mode will be the most accurate reprensentaion of the arrows. So starting there would help.
just know that all of these are details that I feel would help the mod fit better into the game