As someone who did weddings and portraits semi-pro some years ago, I always think that a portrait is more about showing the sitter as they really are. The mechanics of setting up the photograph is, in my opinion, the least of your concerns. Making the sitter relaxed in front of the camera is the really tricky bit. If you can achieve that, you're 90% of the way there.
If you can get your hands on a polaroid back for the SQ-A and show the sitter a couple of test images I found the sitter will feel part of the process and work with you.
Relax and enjoy it. Experiment and don't be afraid to show folks 'warts and all'. Some of us wear our wrinkles with pride!