For the actual building of all the manifests and asset files, take a look at https://github.com/trane-project/trane-music for some examples of how I am generating them. This might seem kind of annoying at first and I wasn't sure if it was the right call at first, but having to manually generate all those JSON files is way more annoying.

If you want to learn the piano, it'd be useful to be able to reference an external resource. I am thinking of mostly using https://www.soundslice.com/ to create the music sheet. There's already a special asset to reference a soundslice link, although it probably needs some improvement (add a description along the link for example). This asset is at https://github.com/trane-project/trane/blob/master/src/data....

Once there's a graphic interface, these kinds of resources could be embedded inside the app so that users don't have to switch context.

But for now, an exercise that says "go practice measures X through Y in this slice at this link" or "practice piece #X from book Y" should be enough to build the exercises.