as a mother and a woman, I'm looking at this from the female angle. your wife is 34 .from a purely physical health point of view she should have another child (if ye are going to do this) within the next two years. You are a primagravida after 35. ( it's not impossible but it does get harder. I know :/
It sounds corny but you won't regret having another child.
It's easy to move kids around until they are four. Once they start school not so easy.
Our kids see their grandparents at least once a week.its a lovely bond to have and in my opinion priceless. Ye have a great income. Ye sound like very responsible people and I admire you for wanting the best for your wife and children. If ye can handle the weather and the crap healthcare, Ireland is a great place to rear kids.
You cannot put a value on the bond with family and community. Good luck with whatever choice ye make.