Thailand is best when the crowds thin out. We like the rainy season for empty beaches and lower prices on flights to Bangkok. You'll eat world-class street food for a few dollars and spend your days hopping between limestone cliffs and hidden lagoons.
The trip usually costs around $2800. If you don't have that sitting in a drawer, you can use a specific card to pay it off slowly. This keeps your cash flow steady while you're busy eating pad thai in Krabi.
The 0% window is a deadline, not free money. If you still have a balance when the 18 months end, the standard interest rate will kick in on the remaining amount. That gets expensive fast, so make sure the balance is gone before then.