Weddingbee boards

You'll have so much fun! 

There's not much in San Jose so if you don't have to spend a night there I wouldn't bother.  You can rent a car but for me I'd find it less stressful to do a shuttle.  Interbus has good reviews, we just took the Tico Bus but it takes a long time (but it's super cheap).  Once you figure out what modes of transport you want it can help you narrow down where you want to go. 

The Nicoya pennisula up north is a bit more ritsy/touristy.  Though we went down to the point to Montezuma/Malpais and it was really cute artsy little towns.  A bit long to get to unless you take a ferry, which is doable.  Manuel Antonio we didn't stay very long but is also supposed to be quite nice, we went down to Dominical which is about an hour or so farther south and I really loved it there, very cute small surfer town.  Those are all on the Western side.  The eastern side I've heard has a much more Carribean vibe and depending on when you're going Tortuguero has some neat turtle tours - I think there are some interesting boat/shuttle transfers they have going between Tortuguero and Arenal so it might be worth looking up.

I really like Arenal, we did an evening hike with William (best guide, you probably can ask for him by name and say the one who hikes the volcano and everyone in the town will know him) and then sat at the base as night fell watching the lava.  I also really liked El Silencio reserve.  It has a really nice view of the volcano (if the clouds happen to part) and we saw several different groups of monkeys as we wandered around.  We just rented bikes instead of a car.  And just a warning if you see a coati and it comes up to you it doesnt' mean it's rabid.  I freaked out as this coati chased me on my bike because I thought it must mean it's rabid but then a car pulled over to see it and it just stood on it's back paws and begged for food, it was just used to people feeding it. 

Oh and bring your own suntan lotion and bug spray.  Most Costa Ricans don't wear it so the price is like 3x higher down there.