The easiest way to get to Kilkenny - the town where the wedding is - for most of you will be to fly into Dublin, and then take the train or a bus to Kilkenny (it's 80 miles from Dublin, ~1.5 hours). Be sure to check the Irish airline Aer Lingus for flights; they do operate out of most major American airports, have non-stop flights from California, and are usually very reasonably priced.
Dublin is the capital of the Republic, the largest city in the country, and home to the largest international airport: Dublin Airport. We are not arranging any accomodations in Dublin, but we will be there for several days before the wedding, and will love to meet you all Friday night (Oct. 11) for snacks and libations (please see the "Events" page for details). If you're looking for places to stay: City Center is close to basically everything, Temple Bar is the bar district and very loud and touristy (think Gaslamp in San Diego), and we will be staying in the Stonybatter neighborhood. But Dublin is pretty easy to get around and there are a lot of great options.
We will not be renting a car, and cannot provide info on car rentals beyond: they drive on the left, the steering is on the right...be safe and good luck. Most of the places we've been in Ireland are very walkable, and in additon to the usual Taxi/Lyft, there's pretty good public transport. Train service runs between major cities, but it's mostly busses, with coach style busses running longer inter-city routes. You should not need to rent a car for any of our events, but you may want to if you decide to explore Ireland beyond what we have planned as some of the "inbetween" places can be hard to get to via train/bus.
Some Hopefully Helpful Links
Aer Lingus' Website: https://www.aerlingus.com/html/en-US/home.html
Bus Service in Dublin: https://dublinbus.ie/
Inter-City Bus: http://www.buseireann.ie/
Train Service: http://www.irishrail.ie/
Irish Tourism Info: https://www.discoverireland.ie/
City of Dublin Tourism Info: https://dublin.ie/