Stay in Bed & Breakfasts, and be friendly towards your hosts, because they will have lots of suggestions of things on that the Tourist Board will know nothing about.
Also, I would suggest picking a region and staying there, rather than trying to cover the entire country within a few days. The roads here are not built for large volumes of high speed traffic, so you physically cannot drive 100 miles in 100 minutes. For rural areas in the west, you will need to hire a car to get around (buses are not great, trains are practically non-existent except for lines between the cities), and petrol is currently €1.16 (at the last petrol station I passed) per litre, and there are 3.5 litres to the gallon, so do the maths. If you don't like driving, I suggest staying in one of the larger cities like Dublin, Cork or Galway, but you could also do okay in places like Limerick, Waterford or Kilkenny - in fact, if you stay in either Waterford or Kilkenny, you can get between them easily by train or bus. It may be possible to do day excursions to places of interest outside the main cities, contact the tourist board for more information, www.discoverireland.ie. Bear in mind that Ireland generally closes down for Christmas.
Northern Ireland is technically part of the United Kingdom, so they still use pounds sterling as their currency there, but the Republic of Ireland uses the Euro. Visa and Mastercard are the preferred credit cards, American Express less so.