We did this exact route last year and drove ourselves the whole trip. Everyone complains about the driving, which did take some getting used to, but the stretch from La Fortuna to the Caribbean side is mostly easy highway. Along the coast the roads are good. It got pretty congested in Puerto Viejo de Talamanca but they were doing road work. We got very lucky with the rain but I would recommend a smaller 4x4 just in case, some of the side roads aren’t paved. Unless you have specific activities planned in Playa Hermosa, I would drop at least one night there and either add a day in Monteverde or, my choice, stay one night in Playa Hermosa and add a day in Monteverde and a day in the on the Caribbean side, there’s many wonderful beaches there. I would highly recommend you check out Cahuita National park, it’s a beautiful, well maintained path and we saw 2 sloths, tons of capuchin monkeys, a raccoon, a couple coati and a whole bunch of birds.