Hi Wayne,
Very cool you’re coming down for a visit. There are plenty of taxis at the Liberia airport. But you might want to check with your hotel if they have some sort of shuttle service, some do some don’t.
As far as getting to Arenal and La Fortuna, you have a couple of options for private shuttles, which will take you door to door. You can reserve your seats now or wait until you get to CR and book through your hotel or by phone.
Interbus http://www.interbusonline.com
Grayline http://www.graylinecostarica.com/
Once at Arenal and La Fortuna you can hire a driver/guide (ask the hotel for recommendations) or sign up for tours to get to the various attractions like the hot springs. There are plenty of taxis there as well.
Good luck and have fun.