1. We chose twitter as the ID layer for our MVP because we think a lot of the creators for who we think Mine will be very valuable have a prominent twitter presence. It was also the easiest to implement in the MVP as an end-to-end example of tying a fingerprint to an identity, and then later being able to recover the identity where the file is consumed. Twitter is also a semi-trusted entity because of its scale, so you can be relatively confident that a creator was the first to claim their fingerprint on twitter. With that said, we strongly believe in the ID layer of Mine being decentralized as well, and envision the future service similar to a Bitcoin wallet, but for file hashes. The public keys will represent the many digital pseudonyms you may choose to have, and files on your hard drive or mobile device will be automatically fingerprinted and embedded in the blockchain.
2. We store the metadata of the fingerprint and the corresponding transaction so you can easily retrieve it whenever you want by submitting the original file again. You can also store the json output yourself, and it has all the information necessary to trace the fringerprint's location in the blockchain. If Mine ceases to exist for whatever reason, all of the "truth" is permanently in the blockchain and the proof json is all you need to verify.