Colombia gives you coffee farms in the green mountains, cobblestone streets in Cartagena, and salsa music in Medellín all in one trip. You want to aim for the dry months between December and March so you actually get to enjoy the coast and the trails without getting rained out.
When you are looking at a $2500 price tag for flights and hotels, paying for it all at once hurts. Spreading out payments can make it easier to swallow, provided you have a clear plan to pay it off.
That intro window is a hard deadline, not free money. If you still have a balance left when those 18 months are up, standard interest kicks in on what you owe.