Late September and early November are the sweet spots for Spain. The summer crowds clear out, the scorching heat in Andalusia drops to a breezy 70 degrees, and tapas bars in Barcelona actually have open tables. It is easily the best time to go.
A typical two-week run through Barcelona and the south runs about $3,600 for two people. You do not need to drop all that cash at once if you spread the cost out over time before interest kicks in.
A 0% APR period is a tool, not free money. If you still have a balance when those 15 months end, the standard variable interest rate kicks in on whatever is left, which gets expensive fast. Set a calendar reminder to clear the balance early so you stay on track.