We advise you to rent a 4×4 car with GPS, due to the state of the road network in Costa Rica. Indeed, the main roads and secondary roads are fairly well maintained, however you will have to take unpaved roads or even tracks and cross small rios.
Your passport and your driving license will be required. You do not need an international driving license. However if you are renting a car when you arrived in Costa Rica, verify that your bank card is a credit card and not a debit card as that does not allow you to rent a car.(noted in small on your card).
There are many car rental companies in San José, but you can also contact the rental companies in Samara.