Hello, Bugatti (nice car!) and welcome. I can't tell you about LGA/MIA loads. There are no holidays around that date, so it would be all the regular traffic. I would consider being prepared to fly to FLL when we can give you more concrete load information. Your plan B should be in your mind before departure. You are permitted to check the same number of bags as a revenue pax. You can find that on Delta.com. I never check bags so maybe someone here can help further. If you each check in a bag, they will not take both since they are different names/tickets. They hold bag until nonrevs get on a flight.
You will be given an S4 priority (like our buddy passes) but you should check in 24 hrs prior (that timing will determine how you rank w/any other zed flyers). We'll be happy to monitor flts a few days before for you fly.
Welcome to the site.