Tokyo is best in the shoulder seasons of spring or autumn when the weather is mild and the crowds are manageable. You get crisp air, amazing street food, and plenty of room to walk through the parks without fighting the peak-summer humidity or winter chill.
Booking four months out gives you the best mix of availability and pricing. If the $3500 cost feels heavy upfront, you can use the Discover it® Cash Back to spread those payments out over time.
The 0% intro APR is a window, not a gift. If you still have a balance after 15 months, the bank will start charging interest on whatever is left, which gets expensive quickly.