@WildPatience and @2024glengardens we are not in Dublin, so no direct experience of finding schools there, unfortunately. We moved back to my home town, and I just emailed the (excellent) local secondary school and they were both offered places instantly.
We never considered TY for the older one, actually. He is winter born so turned 17 a few months after starting 5th year. He was comfortable getting stuck in, didn't want to be 'behind' his equivalent cohort.
In terms of community, my three ( I have one in primary also) have been welcomed with open arms and have great friendship groups, better than the ones they had in London, and I am not worried about them being stabbed on the train to school any more, or being targeted by gangs, etc. There is a huge multicultural mix in their school, and in the town at large, certainly very different than when I left for uni in the 90's. My children are dual heritage, so that was also an important factor for us.
My little one has joined the local soccer and GAA clubs and is very much one of the gang now. These have also been great social opportunities for us too, meeting the patents and getting involved with volunteering and coaching, etc. I've made some really lovely friends too.
The housing situation is pretty shit, especially in Dublin. We are renting, and had been renting in London, so had no equity to move with. I would say if it was possible to move to outside of Dublin and commute in, you'd get a hell of a lot more for your money. There is also a healthy work-from-home and hybrid working attitude here, with companies seeming to accept it more than in England.
Honestly, my only regret has been the lack of decent Turkish or Lebanese restaurants in my locality! I do miss my old Turkish local in London, it was amazeballs!