Getting through/into or round Dublin from Gorey is the big problem in visiting the Causeway
CIE or whatever the rail section is called now do day trips from Dublin Connelly - Train to Belfast - Coach to Causeway and back to Belfast then train. Only problem is getting to Connelly from Gorey - the Gorey Dublin line is slow and infrequent. Would suggest driving to Bray and catching DART to Connelly. Think train is at 8.00 a.m.
Alternative is to fly DUB_LDY and hire care for day. Plane is at 9.00 a.m.but DUB is other side of the city from Gorey and the M50 in the mornings is a car park