Never traveled out of the country before

My husband's CPAP has never been considered as his carry on, because it is a medical device. Here is the link to arrival in Dublin https://www.dublinairport.com/at-the-airport/security/customs-immigration. We have always found arrival in Europe to be easy "nothing to declare". If you are flying home from Dublin to the US, that airport has a preclearance facility https://www.dublinairport.com/flight-information/travelling-to-usa/usa-preclearance/us-customs-and-border-protection-video#:~:text=The%20US%20Preclearance%20(USCBP)%20facility,Dublin%20Airport%20prior%20to%20departure.
I use noise canceling earbuds if it is an overnight flight. A travel neck pillow is also helpful if you want to sleep. On our trip to Ireland, my lightweight, hooded, packable, waterproof rain jacket came in very handy. Ireland is terrific; have a wonderful trip!

My husband travels with a CPAP machine. Because it's a medical device, you can carry it on and it doesn't count as your personal item. So you can bring it on the plane in addition to your personal item.

Enjoy your trip!

Unless you're carrying lots of cash, you walk through customs. You will go through Immigration where you're passport will be checked but not stamped anymore. I assume that you know that there's an entire section of this forum about packing that will be very helpful. You will need plug adapters for your electrical devices, but probably not voltage converters. Ireland is green for a reason, so take good rain jackets. Have a wonderful time!

We use an EPICKA travel adapter that contains both USB-C and USB-A charging ports. You can purchase it on Amazon.

No need for headphones for the tour unless you use hearing aids. Otherwise the guide will provide an earbud along with the "whisper" unit that receives what the guide is saying when you're on a walk or local tour. The earbud is wired into the receiver, not bluetooth, so any headset you might bring for this needs to be wired.

I'd suggest heading to your local library and checking out a copy of "Europe through the Back Door" for a good overview of what to expect traveling overseas. Though you will get an Ireland guide with your tour packet, that's usually only a couple months ahead, so I'd also check out a copy of any version of the Ireland guide to review until you get yours. Note the days you have free time on the tour (it's stated in the itinerary) and do a bit of studying on things you might like to do during that time. The guide will suggest options too but I find it's better to be a little prepared.

I've done the Ireland tour and it is fantastic. Drink the Guinness, visit pubs for music, talk to the people. Can't go wrong.

Besides a good waterproof rain jacket with a hood bring or wear waterproof shoes. If it's windy an umbrella will be of little help. A baseball cap under the hood will also help if it's rainy or sunny. :-)