http://www.buseireann...32129-Network-map.pdf
the map (above) shows the expressway bus network, with the local/regional network overlaid. Note that it's not possible to travel everywhere by local/regional services, but using a combination of expressway and other services it's possible to go almost anywhere in Ireland by bus.
see here for tourist pass options
http://www.buseireann.ie/inner.php?id=279
if a particular place you want to visit isn't on the network, then travel to the nearest town and seek out the tourist information people, who will probably be pleased to help you with your onward plans......