Definitely book at Cahernane. Just email the hotel (booking is not available online!) and let them know you're part of the Curry-Lucks wedding. We've reserved the entire Manor House :)
Up to you! There will be *plenty* to do if you decide to spend 4+ days in Killarney. Feel free to call or text Geoff or Emmie for suggestions. There are also spectacular towns nearby including Dingle (where Emmie and Geoff are spending a couple post-wedding recovery days) and, if you go further north, Galway. The Cliffs of Moher are in between the two and probably the most popular tourist destination in Ireland.
Late Spring/ Early Summer in Ireland is perhaps the best time to visit. Cool in the evenings, warm sunny days, light jackets kinda weather. It probably goes without saying that the Emerald Isle gets its name from the frequent rain (and also the rainbows!) and the weather changes quickly. So be prepared for some showers!
Great question! (lol) If you have data, texting will work, but we are also likely to be using Telegram to communicate group messages. Everyone will be staying at Cahernane, so we'll all be in touch very frequently, but group texting plans for, say, Sunday or Monday evening might be helpful too.