I will try to answer your question. Start at the corner and overlap 3/4 in. This will let the OSB break on the center on your framing. Keep the top flush. Always place OSB vertical. Nail edges every 6" and every where else every 8" The same thing applies to the second floor. On the rim joist just fill in with OSB. Use full sheets and cut windows out after. It doesn't matter where the seams are located,just as long as they break on a stud. Also make sure your walls are square by measureing from corner to corner.