I focused more on the first question, but touched on topics I'd be interested in researching.
For my recommendations, I got both my boss and a former professor. I'm only a few years out of school so it was easy to reach out to an old professor. I'd imagine it would be more difficult to get an old professor if you have been out of school for awhile.
Of course, I still haven't heard back yet, so these may or may not be good tips lol.
Anyone else still waiting? I applied back in early January :/