Hello! That sounds like an exciting trip to Costa Rica. I'm here to help with some useful travel tips.

Best Time to Visit:
Costa Rica has a tropical climate, characterized by two seasons: dry and rainy. The dry season, from the end of December to April, is the best time to visit Sarchí, Escazú, and San Antonio De Belén. This is when you will experience the best weather. However, if you enjoy less crowded places and don't mind occasional showers, the rainy season can also be a good choice with lusher landscapes.

Route and Accessibility:
The Juan Santamaria International Airport in Alajuela is the closest major airport to your destinations. Upon arrival, you can hire a taxi or rent a car to reach Sarchí, Escazú, and San Antonio De Belén. The roads are generally in good condition and well sign-posted.

Accommodation and Booking:
There are a variety of accommodations available in Sarchí, Escazú, and San Antonio De Belén ranging from luxury resorts to budget guesthouses. It's recommended to book your accommodations in advance. The major booking platforms like Booking.com, Airbnb, and Agoda can be useful.

Clothing and Essentials:
Lightweight, breathable clothing is recommended due to the tropical climate. Don't forget essentials like sunscreen, a hat, swimsuit, and sturdy shoes for exploring. Also, a light rain jacket could be useful if you're travelling during the rainy season.

Health and Safety:
Costa Rica is generally safe, but like with any travel, it's advisable to stay vigilant to avoid petty theft or fraud. As for health, no particular vaccination is required for Costa Rica unless you're coming from a yellow fever risk area. Stick to bottled water and bring a small first aid kit.

Local Etiquette and Respect:
Costa Ricans, or Ticos, are known for their friendliness and 'Pura Vida' lifestyle. Dress modestly in churches and respect local customs and traditions. Trying some Spanish phrases can be appreciated too.