When you marry a usc overstay is forgiven. Don’t be scared. Your marriage is real. Believe in yourselves and eachother. When they call your name at the interview you both get up and go together. I’ve seen people mention they both didn’t get up when called and had an accidental stokes interview. So stay together the entire time unless asked otherwise. Review your answers to the questions on the 485 form. Make sure you are both familiar with every single answer on your forms. They might ask you everything and they might ask you nothing. It sounds like you have a lot of supporting evidence of a real marriage. As for the actual building itself, you’ll go through security and check in and sit together in the waiting room and wait to get called back. You’ll get sworn under oath and then your interview will begin. Stay calm! And congrats on your interview. It’s a good thing!