Cocktail attire! Please do NOT wear white or black. Think colorful!!!
easiest way, would be uber. It is available almost all day. Your hotel might also offer an airport shuttle for a fee.
Guatemala uses Quetzales. 1 Dollar is about 7.7 Quetzales, or 100 Quetzales is about 12 Dollars.
lots of places in Guatemala use card readers. So cash is not always needed, but if you want to buy things at the market or leave tips for drivers cash will be needed. depending on the amount of days you are staying. 800-1000 Quetzales (103-130 Dollars), would be enough to get you by!