Spring is the sweet spot for Ireland. Heading over in April or May means mild weather, green hills in full bloom, and smaller crowds at the cliffs and pubs than you get in midsummer.
A typical trip from the US runs about $3,800 all in. Instead of dropping that cash all at once, many people spread the cost out over a year or more using a timed financing window.
Keep in mind that a 0% intro APR is just a clock ticking, not free money. If you still have a balance after 15 months, the regular interest rate kicks in on whatever amount is left, which gets expensive quickly.