Genghis
I wrote an article on this a few years ago that you might find helpful.
Flying in Ireland
One thing that you should be careful of is Irish customs requirements. This has changed since I wrote the article, and unfortunately is very disjointed.
Your obligation (from what Customs tell me) is that you need to inform your airport of arrival and departure (in/from Ireland) that you intend to make an international flight. Some airports may impost additional obligations on you. Eg. Weston want 24 hours notice to the airfiled with details similar to a UK GAR. Other airfields want you to notify customs directly with different time limits.
Galway maybe happy with no notification since they have some commerical flights there. Best to ask about this at least 24 hours in advance so that you know what you have to do (if anything).
Also check the notams carefully. Opening hours can change, as can AVGAS availability. These will be published in the notams.
ATC services available outside controlled airspace is just a FIS. We don't have different levels of service like in the UK. Our FIS is very similar to your old RIS/new Traffic Service. If you use the standard RT from the UK for requesting a traffic service just changing TS for FIS, you'll do fine. RT is much more relaxed here.
As mentioned before, you're likely to be asking Shannon Info for the FIS on 127.5mhz. This covers the whole country outside controlled airspace except under the Dublin CTA.
dp