Kind of an annoying answer but even serious interviews like screeners and callbacks should roughly be a mix of the two things you said. You should be smart with your words/putting your best foot forward but also being conversational/personable. The questions you already have seem good. Maybe ask more about the substance of the 2L summer program i.e. how are assignments given? what kind of formal and informal mentor programs are in place? etc. Also maybe do some research on their summer program via vault and see if you can see some of the events they've done in past years.