Hi Elizabeth
I walked the Dingle Way in April 2008 and Wainwright's Coast to Coast in April 2007.
They are entirely different.
The Dingle Way was very quiet and never far from the sea.
You are sure to have company - almost invariably good company with kindred spirits who will help you if you need them - on the Coast to Coast, which is possibly Britain's most popular Long Distance Path.
Rather than try to tell you everything about the C2C, there are a couple of links you might find useful.
www.sherpavan.com contains a busy message board and a lot of accommodation and planning information.
www.walkingplaces.co.uk also has a message board and several reports of Coast to Coast adventures. My reports on Dingle Way and C2C are actually on there.
The West of Ireland has some of the best coast/mountain scenery I've seen anywhere. As Jacquetta says, it does have quite a bit of road walking. C2C will be a lot of fun, with rugged and steep days in the west, and a great variety of scenery.
Enjoy!