Congratulations and welcome to the forums! I was reading your questions and I see a lot of good answers here. I would just like to add... the sea weed comes and goes all along the coast. You can not really plan for it or where it will be.... only mother nature knows!
Also, Beach restoration is underway in parts of the Mayan Riviera, Playa del Carmen and Cancun... so you may want to take that into consideration for your day.
Best of luck finding a resort for your big day.