Picture the street closed off, kids running between lawns, and the big inflatable bouncy house set up right in the middle of the asphalt. A neighborhood block party takes some coordination, and getting the timing right is what keeps costs from spinning out.
Weekday rentals are usually much cheaper than weekend ones, so locking in that date is your first real move. Once you have the total cost nailed down, you can spread the expense out over time instead of taking a massive hit all at once.
That 0% window is a hard deadline, not free money, so make sure the $900 balance is fully paid off before those 18 months are up or standard interest rates will kick in on what is left.