We hired Gerard Scott at Killarney Guided Tours on two different occasions. He's based in Killarney, so knows the area well. He could also tour you around the Dingle Peninsula (though you'd probably want two days for both the ROK and Dingle).
https://killarneyguidedtours.biz
Then, spend a day in Killarney National Park. Muckross House and its gardens are lovely, and there are lots of hiking options. Wildflowers will be blooming in May.
Also consider visiting the ruins of Muckross Abbey; Ross Castle (just outside town) has really interesting guided tours; boat tours on the lakes are also interesting.
Anyone who gives you a guided tour will know all the must-see stops along the way.
Have fun!