I was just there last month in Playa Santa Teresa on the Nicoyan Peninsula. I would bring a face mask. We rode 4wheelers a bunch and it is super dusty because the roads are shitty there. Bring Teevas or some water shoes too.
We jumped off this sick waterfall that was like a 15 minute quad ride from Montezuma. There was a 10', a 50', and then the last one was a 100' (but looked more like 80). They also had zip lining.
If you are going somewhere from San Jose, try and take a jungle plane. It made a 4 and a half hour drive only 25 minutes and it is super sick views. Bring bug spray and sun screen..we stayed practically in the jungle and the bugs were hell at night.
You are about to have a blast though man. It's without a doubt the sickest country I've been to and also the most beautiful. Bring your Spanish speaking with you, and prepare to be offered a lot of high-quality cocaine.