Do this trip a few times a year by microlight.
Use Haverfordwest instead of Cardiff. London will want an estimate for the FIR boundary where you will be handed over to Shannon and will be given a new squak and they will want you to report "coasting in" at Waterford.
Unless you specifically want to go to Galway then use somewhere else. Galway is not GA friendly and will issue you with fees for "using their airspace !" as well as expensive parking and landing fees.
As other posters have stated there is Sligo/Donegal/Eglington/Enniskillen/Abbeyschrule/Birr/Kilkenny/Clonbollogue/trim/Kilrush and a host of grass strips.
Irish airspace is relatively free class G, except in and around Dublin,so no problem flying here.
The FIS you will use in the south will be Shannon on 127.50, but generally you will work the regional airfields. Parachute drop zones around Clonbologue and some strip where there is busy microlight activity at the weekends.
Drop me a PM if you need anything else...... enjoy.
Jon