Patagonia is all about raw wind, jagged granite towers like the Torres del Paine, and endless turquoise lakes that look unreal in person. You want to aim for the austral spring, between October and November, when the trails start opening up after the southern winter and the summer crowds haven't arrived yet.
A trip like this usually runs around $5000 for flights, gear, and lodging. Spreading that cost out takes some planning so you aren't hit with a massive bill all at once.
Remember that the 0% intro APR is a hard deadline, not free money. If you still carry a balance when those 15 months run out, the remaining amount will start accumulating high interest charges fast.