I’m in Costa Rica right now actually, and it’s gorgeous 🙂
First of all, I wouldn’t recommend going in February-April. It’ll be dry, but because a lot of things have dried up, it won’t be as beautiful. And the beginning of November can still be very wet, so I’d recommend mid November-early February. That is peak season, but as far as I can tell that doesn’t make it any less fun, though perhaps pricier. Also, there tends to be a beautiful break in the rainy season for about 3 weeks from mid-June to early July, but that seems less predictable.
If you want to go to more than one part of the country, you’ll probably need to rent a car, and in a lot of areas the roads aren’t very good, but I know some people like driving on dirt roads. The areas I’ve been to are San José, which is the capital and hot and city-like and not worth visiting but possibly worth flying into, Monteverde, which has an incredible cloud forest with reserves to hike through (go on a guided tour!), butterfly and hummingbird sanctuaries, and Extremo, an amazing zipline course which has a Tarzan swing (the first part was one of the most exhilarating/terrifying half seconds of my life, you’re free falling, but then the harness takes your weight and you swing back and forth a few times and it’s really cool), and a zipline a kilometer long where you go like Superman. They also have a much bigger tarzan swing and bungee but those cost like $40 by themselves, the tour is $40pp and totally worth it. But the cloud forest can get cold, so you’d want to have jeans and hoodies! We stayed at this adorable little hotel, with a cabin with an amazing view of the area, called El Sol, about 15-20 minutes away from everything, but much warmer.
And right now I’m by Playa del Coco, in the Guanacaste region. There are lots of beautiful beaches on the Pacific coast, generally the Atlantic coast is not ideal for tourists, it’s not as safe. Here we have an incredible view of the bay. I also hear great things about the Southern region, like around Arenal, the volcano. Costa Rica doesn’t technically have a lot of rain forest, but it does have a ton of incredible nature and things to do. 🙂