I agree with Mimi's recommendation. Keep your itinerary flexible, stop for the day where you feel like it and be open to the serendipity of travel. It's wise, though, to make B&B reservations for your first one or two nights in country and for the last.
B&Bs are indeed the best and most reasonably priced places to stay, to meet the locals and their families and to enjoy wonderful breakfasts (the "full Irish"). We're going on our tenth trip next summer (all self-planned bicycle trips) and have had nothing but positive experiences in over 150 B&Bs throughtout the country. We've always just shown up in any given town and knocked on no more than two or three doors to get a room for the night. Sometimes, we've called ahead that morning to reserve when we knew in which town we'd be staying.
bandbireland.com has a limited number of listings. You'll find more at ireland.com, the official Tourism Ireland (TI) website. You can also order a free printed B&B guidebook from TI. On the website it's called a "brochure" although it has 56 pages of county by county listings.