Ireland is awesome, I went there last summer, but not for a surf trip. It will be a great trip, but I wouldn't go in the winter, because there won't be much daylight hours as Ireland is very far north. Think about planning a trip there in the fall or spring time.
Rent an RV and plan on doing a lot of driving. Huge tidal swings cause spots to turn on and off within a few hours. I surfed near Easky one day. Wasn't there on a surf trip but had brought my stuff anyway. Got a really fun right hander with only a couple of other guys out. The ocean and water temps aren't much colder than the NJ area, although the rain might get old after a while.
Agree with swellinfo. Biggest waves in winter but with 6-7 hrs of light and most likely howling onshores your best bet is Sep/Oct or Mar/Apr. Summer can be flat except for a random swell. I would defo say April is the best month for a trip. Waves consistent enough, long days and occasional offshore spells. Oh yeah and the tides are huge most everywhere. Upside is the possibilities of finding a wave to yourself are boundless.