Si no recuerdo mal, nos costó unos 50 dólares por persona, per veo que eres de costa rica, por lo que tu precio será más barato seguro!

We were there in Feb / March, didn't have a mosquito problem, but we were wearing natural repellent just in case

Lo desconozco, nosotros arrendamos auto y llegamos con waze.

No. You can purchase tickets onsite at the welcome desk. Please note that this is an Animal Sanctuary. They care for animals and birds that cannot be rehabilitated. So they are all in cages. The park is beautiful but if part of your reason for going is to see animals in the rainforest you may want to be aware this is more like a zoo.

The waterfalls are not wheelchair accessible due to stairs required to enter and exit. The stairs are step and small wooden blanks with wood railings on both sides with traffic going up and down. The gardens, restaurant. Cafes and shops are wheelchair accessible. Prior to waterfalls are animals such as exotic birds, monkeys, butterflies. Nice 1/2 day visit even if you can’t see the waterfalls

There is secured parking. Your belongings will be safe.

There are other sanctuaries such a Zoo Ave which are a bit more open but still have cages. In La Paz Waterfalls the animals have been rescued after having been run over by cars while trying to close the street, being kept as pets illegally or while in an attempt to smuggle them. The government has handed them over to la Paz, because they do not have enough budget to care for them themselves. My brother has worked for the hotel and he certifies that they get the best food and receive regular veterinary visits. During the Cinchona earthquake in 2009 many cages and enclosures were badly damaged and hotel staff and vet chose to stay with the animals for over a week, even though they were urged to evacuate the area and leave the animals to their own fate. You can choose to visit national parks such as Corcovado or Manuel Antonio, where you have a better chance of seeing animals in the wild too.

It is a self guided tour.

Around 4 hours would be plenty of time.