I'm a Mexican national, residing in the US. What am I required to enter into Guatemala other than a pport?

Mi plan is to fly into Mexico City and rent a car to visit the lower states of Morelos, Guerrero, Oaxaca and Chiapas; then turn the car in and enter Guatemala and travel by public bus to San Benito, Pet�n, Guatemala (Tikal)and on to Belize City and further into Mexico's state of Quintana Roo to rent another car to continue trough Yucatan, Campeche, Tabasco, Veracruz, Puebla and back to Mexico City. My goal is to visit as many Mayan, Olmec, Toltec and Aztec ruins as I can; with a couple of cool beaches along the way in a span of 3 to 4 weeks. I know enough about Mexico and got information on the car rental to feel safe. Can someone give me pointers about Guatemala and Belize?