Well, there's a lot of Irish mythology in there already. Fairies, leprechauns, clurichauns, St. Colman's ducks, the list goes on. But we didn't limit ourselves by Irish mythology, of course, because the world is bigger than Ireland, and even the wizards of the Isles don't really differentiate by nationality and just consider all the British isles as a single cultural entity.
As for the House names, they are vaguely based on different locations in Ireland and Scotland with the attributes we felt relatable to the Houses.
edit: Oh, forgot about the names. We mostly just though of the names that we felt right for the characters. Some of the names I had in mind already like Gwen, Elizabeth, Lily and Violet. Also, Lardbee, the groundskeeper and Professors Dulgren and Mooney. But for more "exotic" names, I usually task Shady Two to come up with some names, and then we decide after she returns to me with three or four variants.