I know I am biased beacuse I live there but Rosslare Strand is your best choice. I bought what was supposed to be a holiday home there 5 years ago, moved in for the Summer, and never left!!!
Really great sea side resort which hasn't been overcome by amusements, louts & sticks of rock!!
27 hole Championship golf course, 4 miles of beach, childrens play area, Woodtown Open Farm, Kellys Resort Hotel (check their website- superb hotel with €7m seaspa), Bradys Bar, Cedars Hotel, Chinese, and a beautiful French style Patisserie all in the village centre. You are still only 10 mins from Wexford town, and there is a train station in the village also if you didn't want to drive.
As I said I am probably biased but it really is a beautiful place which always has a holiday type atmosphere, and it is frequented by some of the most well heeled of Irish business (Kellys Hotel attracts them all). In terms of self catering there is an abundance- you could try Self Catering Ireland, or Menapia Properties 053 9131272 for assistance.
Best locations in the village are Strand Rd, Station Road, Woodtown or The Burrow as they are beachside & you could walk everywhere. Rosetown is bit far out, while Grange Road would be approx 0.5mile walsk to the beach.
All the best hope you enjoy it!