Late September is the sweet spot for Banff. The air is cool, the summer crowds have gone home, and hotel rates drop noticeably while the larch trees turn a brilliant gold against the rockies.
We need a solid plan to handle the roughly $2000 price tag for this trip. Spreading out the cost can make it manageable if you want to lock in your dates now and pay as you go.
That 18-month window is a hard deadline, not free money. If you still have a balance left when it ends, the remaining amount will start getting hit with regular interest.