A quick remark: Watch out for building too many small apps. Just like with building too many websites, at some point you're unable to maintain all of them as customers will demand updates/add-ons.

I think you need to focus on:

- Potencial audience - Is that audience one that will be willing to pay? - Does the price times the potencia sells, worth the effort?

With those three points you can start.

There already is a site dedicated to arthouse torrents: karagarga.net