Aer Lingus is the national airline of Ireland and operates daily direct flights from Ireland to the USA serving multiple locations. Jet Blue & American Airlines also fly directly to Ireland.
Again we would recommend Aer Lingus. Ryanair is a low cost airline that operates from most major European cities to Ireland. We recommend using Kayak.com to price and look for flights.
In Ireland we drive on the opposite side of the road to the USA. Note that rental cars in Ireland are generally manual transmissions. If you want to drive an automatic car when you are in Ireland please ensure you book the correct car.
If you fly into Shannon your only option would be getting the bus from Shannon to Killarney if you chose not to drive. Please note this bus is not direct and would stop in Limerick. There are more options if you fly into Dublin, you can get the bus or train directly to Killarney from Dublin City Centre. Alternatively you could hire a car service from either airport and get dropped directly to your hotel.
We would recommend working with your cell phone provider to enable your current phone plan for international use or risk incurring a sizeable cell phone bill . Alternatively if your cell phone is unlocked you can call into any local phone shop and purchase an Irish sim card. Note all phones will work when connected to Wi-Fi, most business provide Wi-Fi access for customers.
Ireland uses the Euro. Work with your bank/credit card provider to see if you incur any foreign transaction fees prior to departure.
For Ireland the associated plug type is G, which is the plug that has three rectangular pins in a triangular pattern. Ireland operates on a 230V supply voltage and 50Hz. We would advise purchasing this on Amazon prior to your departure.