Hi Jim,
Adobe and Vamos 4×4 should be fine. I meant avoiding some of the small, “unofficial” car rental operators you might meet on your travels.
Drive time from San Jose to Jaco is about 1 1/2 hours on average. For the other times, or hundreds of other routes, check out this site. It’s an excellent drive time calculator and has good maps too.
http://www.yourtravelmap.com/costarica/travelmap/index.php
In Arenal be sure to check out one of the hot springs, hike around the volcano – the national park has good trails, and have lunch on the lake – Café y Macadamia is my favorite spot. If you’re scouting real estate though give yourself an extra day just for that.