Hi, and welcome to the group! I'm very jealous of your trip - my father is Irish yet I've only been to Dublin once and down to the South-West of the country once. There's so much more of it to explore!
I certainly had no trouble finding vegetarian food when I was there though, as with everywhere else, you may find vegan catering a little harder to come by. I know the place I stayed in Goleen did a vegetarian and vegan version of their breakfast though as I think did our lovely B&B in Kilkenny. Gluten-free is widely recognised both in the UK and Ireland though again, I'm not sure how the land lies on that when actually eating out in restaurants. Supermarkets and even smaller food shops generally stock a wide range of gluten-free versions of many foods.
Do you have a specific itinerary set up yet? If so, I would certainly highly recommend emailing all the places you're staying to discuss your dietary requirements. Many places will be happy to cater as long as they know in advance.
It sounds like you've certainly done your homework on here which is going to be a great start for you.
I found the following links which may be of some use to you:
http://www.vegetarian.ie/content/galway-vegetarian-group-monthly-meeting
http://www.meetup.com/vegetarian-485/
http://homepage.eircom.net/~veganirish/vegan%20groups%20ireland.htm
Hope those might help.