I’ve been to a few of the Iberostars resorts and the Occidental Grand Xcaret. You can’t go wrong with any of them. The Occidental is next to Xcaret and includes one day admission. I don’t know about dive operators in Playa del Carmen, I’ve heard the diving isn’t great but you could always go to Cozumel via a 45 minute ferry ride. Great diving there and lots of good dive shops.