Oh man you are going to have a blast. I got addicted to Costa Rica from 1996-2009. Went twice a year sometimes. The little place where I always stayed got sold and made into condos, and that whole area around Quepos is getting more and more developed. I decided to quit while I was ahead with the great memories I had. Very good people the Tico's are. If your car breaks down or gets stuck, someone will stop and help you right away. I could go on and on Ramie but one small tip, breakfast will include beans and rice (HARD working people, they need energy) which I love, and lunch is the biggest meal and the typical restaurant will have a special they call "Casado" like a big home-cooked blue plate special for just a few bucks. Beef is likely to be tough but fish and chicken are great. Also if you see any kind of "albondigas" (meatball) soup or just about any soup, they are always so good and a huge bowl and they will ask you if you want an egg cracked in it or not. Service is not that quick though. Tip is included but I always left extra, after all these people have families to provide for.
Regarding driving, the roads are awful, be careful but once you get used to driving there, it is fun! You'll notice the Tico's will patiently stand in long lines at a bank, but as soon as they get in the driver's seat of the car, they become race car drivers!