All good advice! I would add that you need to have a few thoughts on future research projects with your POI. This was hugely important for my interviews. It came up so many times, and not only with my POI, but other faculty members as well. Especially great, were the times other faculty would get excited by the fact that I had some ideas and they wanted to contribute to them!
Other than that, relax and be yourself! Because the truth is.... we want to impress you as much as you want to impress us. So generally, interviews will be a bit more relaxed than you anticipated. Yes, you will have that one awkward interview with a faculty member, but it isn't the end of the world. It is only one person. And try to enjoy it! You are in your dream situation, talking to experienced people in an area you want experience!! Take advantage and Good Luck!