Went to Costa Rica a year ago, stayed in RUI Guanacaste and went with TUI, they fly direct to Liberia. TUI do loads of excursions as well as other operators there - if you look on their website if will give them. Arenal is often one of the most recommended places but was a pleasant trip to volcano and hot springs but least favourite. Favourite trip was with Gecko tours just us , they are on the beach at RUI, went to rainforest with 2 guides and got to cuddle a sloth. Also went to Diamante, kids and DH did zipline which goes at 60mph and starts at crazy heights, lots of animals there too, they loved it, that's next to RUI.
At our hotel you could kayak, windsurf and SUP included in AI, there were 5 raccoons, 1 coati, hanging round hotel. Monkeys just outside by beach. We to Buena Vista trip, lots of fun, waterslide through jungle then ziplining through jungle by active volcano, monkeys and toucan in trees, horseriding and hot springs. Another trip to Blue River with Nexus, about 8 of us, lovely gardens etc.
Driving, we were advised not to hire a car and tours drove through rivers and no road signs often. Lady said her cousin did it and ended up lost for hours. Not been to San Jose or Belize. Monteverde has hanging bridges but wasn't sure for kids. Beautiful country loads of wildlife would recommend. RUI great food, even kids got 3 course meal served by waiters on AI with steaks the size of the plate 😱 great facilities but very lively so not for your quiet holiday. 😎 My DS is ASD so a strong preference for AI and one jotel.