US citizen and US PR getting married in Mexico, requirements?

My fiance is a US citizen and I am a US Permanent Resident. I was born in Mexico. We want to get married this summer in Mexico. Not sure exactly if it will be Playa del Carmen, Riviera Maya, etc. But we want to know what the legal requirements are and if the civil ceremony can be performed on the beach. It will just be the two of us and we only want to be there for about a week. Is a wedding coordinator neccessary?