It is a pleasure enough that you want to join us on a long trip in another country to be present at our wedding. Don't make it weird by also offering a gift.
The closest airport to Westin Costa Rica is Liberia International Airport (LIR), also known as, Daniel Oduber Quiros Internacional Airport. There are direct flights from Miami, Houston, Atlanta, Los Angeles, New York, Dallas, Charlotte and Chicago. Outside of those cities, you will need to take a connection flight.
Yes! You will need a passport that is valid over a 6 month after the trip to Costa Rica.
We would not recommend renting a car unless you are comfortable doing so as some roads in Costa Rica can be difficult to drive on.
While credit card (visa) are accepted almost everywhere, USD are accepted most places, if you decide to exchange some currency to colones di it at the bank due to exchange rate it is best. American Express is not accepted in most places of Costa Rica.
Check with your local provider for phone options, some carriers will have international plans that you can purchase ahead of time. You can also op to not get an international plan and just use your phone via Wi-Fi connection.
Top 2 things: passaporte and sunscreen. We will basically be on the equator during their summer and the sun is very strong.