September is the sweet spot for the Scottish Highlands. The summer crowds are gone, the midges have largely died down, and the heather on the hills is turning deep purple before autumn takes over. It is the best time to rent a car, drive the single-track roads through Glencoe, and actually hear the wind instead of tour bus engines.
A typical trip runs about $3,500 all-in for flights, lodging, and car rental. Spreading that cost out over time makes it manageable, but you need a clear plan so you do not end up paying high interest rates once the initial window closes.
Remember that the 0% intro window is a strict deadline, not free money, and any remaining balance at the end of the 18 months will be subject to standard interest rates.