You want the food hot and the tent set up before the first guest pulls into the driveway. Start by locking in your catering and rental vendors three months out so you are not scrambling for scraps when the graduation season hits.
A party like this usually runs about $950 for the essentials. If you spread that cost out, it is manageable without blowing your monthly cash flow.
The 0% intro window is a tool, not a gift. If you have a balance left over when the 18 months are up, the bank will start charging interest on whatever is still owed.