Wow, that's so exciting! I am happy to hear it is not very formal actually, the more relaxed the better in my opinion. I definitely have looked at first year students work and feel prepared to ask them more questions than the faculty so far. I think the best thing for us to do is relax and not get overwhelmed. We are going to do great, don't be nervous! Easier said then done, I know. Send me a message or something and maybe we can meet up for a celebratory drink after we complete the interview! Good luck!!!