A backyard dinner is about the people and the atmosphere, not a mountain of debt. Since you are hosting in early summer, start pinning down your guest count and menu now to avoid last-minute price spikes.
Break the $3000 budget into manageable chunks. You have 18 months of 0% for 18 months on purchases and balance transfers from date of account opening to spread out the cost, but treat it like a monthly bill rather than a distant problem.
That 18-month window is a deadline, not a gift. If you still have a balance once the offer ends, the remaining amount will start accruing interest at the standard rate, which can get expensive fast.