Everything on the ship is cashless. You will have to put cash or credit card when you check in. Your room key is also your "charge card" while on board.
Progresso has a the longest (I think) pier. You ride a bus into town. The open air bus is fun and they stop at various "drinking" places and they people try to get you to come back. Since yall are drinkers, that might be fun for yall.
Cozumel, you dock right close. Several bars right there and lots of shops. We did a jeep tour around the island last time,but it takes all your time if you wanted to shop much. It was really fun though. We booked before we went. Just pay attention to the time (ships time). We have watched many a people that had too much to drink get left. They will leave you
Don't forget to bring a small wrap because the dining rooms and shows get chilly.