OP has already booked but in case anyone else cares to read a bit more, I vacationed in Playa del Carmen this past February.
Flying into Cancun from ORD was fine, no problems there. Customs and immigration inspections were effortless and breezy. I took the ADO bus to Playa and I’d highly recommend it to anyone. There’s a counter to buy a ticket immediately after leaving the customs area. There are a few different spots to wait for buses but they gave very goods instructions at the counter as well as ADO uniformed personnel wandering about to answer questions and help with luggage.
The bus station in Playa is in a pretty good location, right in the thick of things. We (five in total) stayed in a smallish hotel (about 30 rooms) right on 5th Street which is sort of the Bourbon Street of PDC, though not nearly that bad. There are plenty of great dining and drinking options up and down the street and within a few blocks parallel. I’d previously been to an all-inclusive in Cancun which was really nice but, for this trip, I feel like we’d have missed some very special little spots had we not wandered about.
Take the Ultra Mar fast ferry to Cozumel ($18 R/T) but have a plan before you get there. After arrival on the island, dodge the crowd of folks luring ferry passengers to rental cars, jeeps, scooters, tours and stuff to grab a cab to your destination. We went to the island twice, one place was sort of quiet and good for laying around on a sandy beach. The other (I can’t remember the name) was more lively and a great time. The first day, there was a fantastic band and it appeared to be mostly locals enjoying the Sunday evening. I had the best octopus I’ve ever tasted there. The second day, there were some HUGE cruise ships docked on the island. It was not quite so nice with all the people but we did some snorkeling which was truly amazing: barracuda, rays, anemones, bio luminescent … jellyfish(?), fish of every color except the dull ones, elaborate corals. It was like a Jacques Cousteau film and I’ll never forget it. Or that grilled octopus. Or my sunburned back. Or the loud American cruise ship passenger that got a sea urchin spine broken off under the skin of her finger…somehow.
One of the days were were there, we took the colectivo (sort of a bus system) south to visit Dos Ojos, a system of cenotes. We did a snorkeling tour there. It was awesome. Freshwater caves, sparkling fish, bats, impossible rock formations, really fun. The guide that drove us from the welcome center to the cenotes commented that we had arrived during the dry season and that the jungle that the dusty road cut through would explode with greenery after the rains and I do wish I could have seen that. The colectivo system seems well established and a lot of people were using it, though the vehicles seemed to be mostly minivans and small shuttle buses so our group got split up. My poor Spanish language ‘skills’ were tested on the bus but I came out just fine.
Every step of the way, I was touched by the kindness, warmth, patience, and humor of the Mexican people. English fluency was good or better in Playa, a bit more challenging further out but still manageable. The flight and room were priced fairly but, once on the ground, everything was very, very inexpensive. The peso:dollar was about better than 19:1, even on the street with fees and whatnot. Walk the beach, find a nice quiet spot, approach the loungers, pay 50 to 100 pesos for use of the chair (includes one drink!) and then 200 pesos for buckets of six beers, limed, iced and delivered. Motion to one of the roving abuelas for a cup with more mango than one person can possibly eat for 50 pesos, chile, lime, and salt included but optional. The colectivo ride was an insanely cheap 45 pesos, barely more than $2 for a 40 minute ride. Renting snorkeling gear beachside was about 15 bucks for all day on Cozumel.
OP: I have a demand. After the ADO bus drops your off, take the short walk to La Cochi-loka for the best goddamned torta you’ve ever had. Worth the walk, luggage and all. It is a little window in a hotel courtyard featuring cochinta pibil, a roast pork specialty of the region. Of all the excellent bites I had in Mexico, this was the best time & again. I ate there about 4 or 5 times. Bring your food to the adjacent Ranita bar. The lovely courtyard is in the back though the bar is great, too.