You are picturing the toasts, the room full of people, and the relief of actually pulling off a great retirement party. A Sunday venue booking keeps costs reasonable, but you still need to pull together about $3000 for the food and space.
Big events live and die by the calendar. Booking early gets you the date you want, while catering counts can usually wait until a few weeks before the big day.
Remember that the 0% intro window is a deadline, not free money. If you still have a balance left when those 18 months are up, regular interest will kick in on what is left.