Everyone worries about driving on the left. In practice most people adjust within an hour. The things that actually catch Americans in Ireland are the width of the roads, the rental-car insurance, and trying to drive west on the day they land.
Start with the insurance, because it is the part that costs real money. Many US credit cards exclude Ireland from their rental-car coverage. The ones that do cover it usually require a printed letter confirming it, and the rental desk will still place a large hold on your card. The alternative is the rental company's own super cover, a daily charge that removes most of the excess. I sort this out before you land so nobody is deciding at the counter.
Then the roads. Outside the motorways, Irish roads are narrow, hedged and often shared with a tractor. A small automatic is the right car, a mid-size SUV is the wrong one, and the drive times on the map are optimistic. I plan two or three bases so nobody drives more than three hours in a day.
The first day is the other trap. Flights from the US land in Dublin around six in the morning. Picking up a car and driving to Galway on no sleep is how the trip starts badly. Day one is Dublin on foot and an early night. The car comes on day two.
For some groups the better answer is a driver-guide. Three generations, a golf group, or anyone who is dreading the left side will have a better week with someone else driving. It is a real cost, and I will say plainly whether it is worth it for your trip.
One more thing about the north. Belfast and the Antrim coast are two hours from Dublin and belong on the same trip, but Northern Ireland is the UK, and US visitors now need the UK's electronic travel authorization even when they cross by road. It is a small fee and an app, and it is on my checklist so it is not on yours.
