The place is living up to its billing in two particular regards: endless variety of colorful birds, pretty much everywhere (even inhabited zones), and more green than can be seen. This looks like the place to rack up numbers of birds sighted, breaking a sweat but barely having to turn one's head.
Also, the traffic in San Jose (do you know the way?) is just as bad as promised.
When it's hot here, it's hot like nowhere I've been (OK, maybe like India when it's hot there). It isn't always, though, which gives hope.
My advice is to plan for a recovery day in a decent hotel with A/C and TV after about every 2-4 days in the rustic eco-cabins. One has to do laundry about that often, anyway.
As far as traveling around in the country, the better way hasn't yet emerged. Perhaps one of those services where you pay a monthly fee, then pick up a car or SUV when you need one. That way you aren't stuck waiting for buses to pick you up, driving whenyou don't want to, or taking dangerous dinky planes or unseaworthy boats.