Your selection of good coach seats makes zero difference. You will be upgraded on those empty F flights. If it were me, I would start the check in 24 hours prior to the flight, but only proceed as far as to get put on the F waitlist. The next day, if you view your itinerary online you will likely see yourself already in F, and can then select your optimal seats, and then do online check-in all the way through including printing out your boarding passes. If F is really that empty, you shouldn't have to wait till you get to the gate.