Sounds like a great trip. I explored the Nicoya back in January. Some tips for the car ferry.. get there a couple of hours prior to scheduled departure to ensure you get a spot on your desired ferry. Watch for the guys directing traffic. They’ll direct you where to get in line for boarding the ferry. Then they will give you a voucher. You have to take that to the ferry ticket office and buy your car’s ticket, as well for any passengers. Then head back to your car and wait for the signal to board. It’s a very smooth process.
As far as driving on the Nicoya Peninsula, it’s dry season so the road conditions should be pretty good. Highway 21 is paved, although the smaller roads will be a mix of pavement and dirt. I would recommend a 4WD SUV as some of the roads on your route could be rough (still passable) and it’s possible (especially if you get turned around) you might have to cross some rivers or creeks without bridges. (Ask your rental company if this is permitted.) Also, definitely get the GPS and rent a cell phone.
This time of year it’s also possible to drive all the way up the coast on Highway 160. Although always ask locals about road conditions before setting out. You’ll see some beautiful stretches of coast here and can easily pop in to check out Samara, Nosara, Malpais and other beach towns. It’s probably advisable to stop for the night in one of those towns so you’re not on the road after dark. Sunset is at 530 approx. This route does feature all dirt roads, some rough patches, and you definitely have to cross multiple rivers, some knee deep. It’s an adventure for sure.
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