I've heard good things about the Air bnb's in C.R. Great choice spending the first week in the cloud forest. I lived with a family there for 2 weeks while I went to language school. It gets chilly up there!
If I remember, I used a credit card for hotel bills and car rental, and cash for everything else. Remember there is the departure tax. You know you can pay for everything in dollars, and they will give you change in colones...the two are interchangeable. I got a sheaf of one's from my bank so I'd always have them handy for tips. As for how much cash to bring, I don't know what the prices are like there anymore.