This is our wedding website - if you are part of the Irish contingent, it basically has all the information you may need for the wedding. If you are part of the American contingent, you know what's up.
No, tipping is not customary like it is in America.
While most places accept credit card, we recommend taking out some Euros during your stay. This will make things like paying for drinks or taxis much easier.
Publicly available wifi is much more common in Ireland than the US, including on transport. It may be helpful to purchase an international data plan, but it isn't necessarily required.
The ceremony and cocktail hour will be held outside, weather permitting. Dinner and reception will be inside.
Hotel check-in begins at 2:00 pm, so be aware for you arrival time.