Buy a SIM at the Kiosk in the airport. You will need Data, not just Calling. Your phone needs to be Unlocked as well.
It is easy enough to get there with a map the rental car agency provides. What did 2 million tourist a year do before Smart Phones? They read the map.
Zika is hardly an issue or risk, but consult the CDC for updates. Dengue is usually the main risk, but that is more in low lying coastal areas in rainy season, more on caribe side. Its hot and dry now in most of CR.
Adventure Travel to Colombia, Costa Rica, Nicaragua, Honduras, Guatemala, Mexico, Thailand, Burma, Laos, Cambodia, Vietnam, China, South Africa, Morocco, Turkey, EU, USA National Parks, enjoying culture, cuisine, motorcycling, scuba diving, surfing, sailing, rafting, hiking, fishing, camping, nature, wildlife. Get a Guidebook, and get lost!