Do not bring a bunch of dollars. Use the ATM. The Cambios make a profit selling you pesos. There are ATM's at the airport past customs. Notify your bank where you will be.
Use your credit card for large purchases. If you do use a credit card stay with it and keep it in sight.
At the clubs, pay for your drinks as you go. Learn the servers name and use it. That part of Mexico is very safe, as in any tourist area, be smart.
There are all kinds of side trips; Maya Ruins, nature parks, zip lines, snorkeling, shopping, bar crawls, dance clubs, shows...
It will be hot so prepare for that. Put on your sunscreen BEFORE leaving your hotel room for the beach (one hour) like it says on the tube. Many people get a vicious burn and spend an uncomfortable week.
From The Grand Oasis the best way to get around the Hotel Zone is the bus. Get coins from your front desk.
We live there in the winter. Feel free to PM with more specific questions.