1) That kind of targeting is even less useful outside of FB. You can upload gmail addresses to Google to target, or use something like LiveRamp to target on display networks, but both options suck compared to FB.

2) Nothing beyond whats publically available.

3) It's not unusual to test different audiences, I've definitely tested all sorts. I'm sure thats how it started for Cambridge. Of course now, tin pot dictatorships hire them all around the world now to be basically a subpar FB agency, so they're happy with the PR.