Mr.PhD

Hello, I received an email a few days back regarding setting up an informal interview with one of the PIs i listed in my SOP. The interview is in 2-3 days (Still not confirmed yet). The research of this PI is AI and mathematical optimization focused. So a good combination of theory and application. How should I prepare for this interview? i looked online and saw some typical question i should have an appropriate answer to "why do you want to do a PhD", "tell me about one of your projects", and I should also have a good idea of his research. All that is fine but this is one of my top choices so i really dont want to mess it up. I wanted to post here to gauge the big questions that i should really know about and things I should keep an eye out for. What exactly might the PI be looking for here? What are must know prep. questions i should know? should i expect any technical questions? I do not expect any coding questions as the lab is theoretical but I can never be sure. Also how prepped i should be for like of the shelf linear algebra, real analysis questions. Any insight would be very appreciated. Extra context: The school is in the U.S and the program is a PhD computer science program. The time frame is arranged for 20 minutes. Also, I thought about contacting some of his students to ask them if they might have some tips for the informal interview and see what he usually looks for in interviews (maybe he interviewed some of them). Would you recommend I do that? I thought about it, but I'm scared if it might reflect badly on me if he gets to know I'm contacting his students for interview prep. Thank you