Paul, it’ll be a great trip, to a great destination. For what it’s worth, on 2 trips so far, we’ve kept each one to just a part of Ireland. The only common denominator locations have been Galway/Inishmore (largest Aran Island) on both trips. Both trips began by flying into Dublin Airport, then immediately catching a bus (coach) to Galway, where we checked into a B&B. Our first trip, going down the west coast from Galway to Dingle, then on to Skellig Michael before turning north to Limerick then the Shannon Airport, was mostly by bicycle, so not moving that fast, and not trying to cover too much ground. Second trip, late September/early October 2 years ago, involved flying to Inishmore after Galway, rather than using the ferry we’d used on the first trip. Flying’s definitely the way to go - faster, and not subject to rough-water delays or postponements that happened for boats both trips. Then on the second trip, we drove clockwise, around then up to Northern Ireland, and around, eventually, to Dublin.
Beehive huts atop Skellig Michael were a treat, reached by a long stairclimb past endearing puffins. This was in June 2011, before Star Wars fans started booking up trips to see the site that appeared in one film. Book your boat trip early, and hope for smooth enough waters to allow crossing out to the island for the day.
Giants Causeway was also fantastic, but so far north that we didn’t include it in our first trip, which stayed farther south. With a car and time, you may have a different itinerary. We stayed at a B&B a bit east, east of Bushmills, and hiked to the Causeway in high winds - thrilling views the whole way. We took the free shuttle bus back to where we’d parked our car for the hike.
We hired local Neolithic expert and noted author Anthony Murphy for 2 days to show us sights including Newgrange, and he added more historical insight, and pointed out more mysterious rock carvings, than we could’ve seen on our own.
Haven’t stayed at any Irish castles, but don’t miss the Hawk Walk experience at Ashford Castle, detailed in Rick Steves’ guidebook (opt for the Extended Walk, which includes their Eagle Owl, too), and the magnificent castle in Trim, a wonderful town for a base while visiting Boyne Valley ancient historical sights.
I don’t believe “crazy hot” ever happens anywhere n Ireland, but you can be assured it’ll rain on some point in your trip.