That's what I basically did, too. I used
ptmod to convert a royalty-free midi into
a mod (sounds ugly, but at least it's legal

I do not package any other mods with the game itself,
but put them as zips on my page, example
.
In the zip, I put a readme with the name of the author
and the place on the web where I found the mod.
The major difference between your and my concept
seems to be that you intend to package those mods with
the game from the start. I would love to do that, too, since the mods I found are way better than anything I could put together (just listen to the
"caveman"-mod, you will feel like playing Donkey Kong
Country

Best regards,
Jens