What a lovely trip report - I really enjoyed reading it.

Would be glad to answer your questions. I think short raincoat is probably adequate. Long one is so much trouble to carry around. Just expect to be wet at some point and quick drying pants, rather than jeans, good to wear on rainy days.
We definitely enjoyed Howth and Newgrange. We had bought and studied the Rick Steves guidebook and he only mentions two options for NewGrange (a local tour company and a bus option). I should have done more web research -- once in Dublin at the tourist office, we realized there were several tours operating in the area. We took Grayline because it was easy pickup near our hotel and actually gave us the most hours. Grayline provided the Newgrange ticket; not sure if those can be pre-booked.
Howth was lovely and we did not have enough time there. But the Grayline tour did provide enough time at both Newgrange and Hill of Tara.
Definitely prebook Kilmainham Gaol tour!! We missed out on it because they were sold out for the afternoon and morning we had available.
I did prebook an Abbey theatre ticket for us also but that was the only thing.
Enjoy your trip!

Thank you so. I have for including so much detail in your report, and for your honest assessment s of the hotels, meals, etc. we hope to visit Ireland next year and I will save your report to help in planning.