Agree with Dexysgirl, the best way to do Westport would be on the return leg. Go to Galway, head through Barna, Spiddal then on to Inverin, maybe Carna, Carraroe and then on to Clifden. or through Moycullen, Recess and then Cliden (stop off at Ballynahinch Castle on the way) Heading back from Clifden, go to Westport then back through through Tullycross via Renvyle, Lettermore, Letterfrack and pass by Kylemore (amazing spectacle), then on to Leenane, then Maam up through Corr na Mona, then Clonbur and finally have a tea in Cong and Ashford Castle and then head back.
Any more questions throw them in !!