I'm envious!! It's on my bucket list, haven't got there yet though. What a journey that'll be. That kind of tour can be exhausting, but who cares when you're seeing a ton of sights, places where history was made? As for your friend's remark: Some people just don't realize that other people choose to live within their means. Fact is, the way to see Ireland is ANY WAY YOU CAN. I'm betting you will have a whale of a time and you will meet people. If you reach a point of overload or fatigue, there is no law against asking "what time does the bus leave?" and going for lunch in a local instead of touring another castle or church. You're fairly likely to meet one or more like-minded folks on the tour who'll do it with you.

If you can, it might be good to take notes about the gist of all that is said by tour guides and others. Keep a photo list, not every single photo, but maybe every 5th or 10th photo and others you want to jot about; it'll help you put any forgotten things into sequence & context when you get home. I didn't do that for a fast-paced tour we did of London & Paris. (As in: "What the heck is this and why did I take a picture of it?") I learned from that and did keep an outline list for St. Petersburg, and it made me able to organize photos and historical info in brochures quite efficiently. Well, more efficiently.

S'gonna be great! Have a lovely time.