This question is mostly for people doing benchwork, such as molecular biology research (which is what I do). What tips can you give me about how to be as efficient as possible when you're at the bench, to get everything done as quickly (and effectively) as possible?
Is there anyone else in your lab who could help you figure this out? Such as someone who has already done interviews (or job applications) and would have asked your PI about this same question? Has someone from a recent year already joined a PhD program and also worked on confidential research? You could email them to ask how they handled it.
Some schools will have you interview with up to 8 faculty members, so there's nothing wrong with asking to meet with all of those people. This is probably more the case with programs that have rotations though. Although if it's a program that admits you directly to a lab, then it's even more important to meet with all of the people whose lab you might join, since it's a huge commitment for both you and the faculty member.