You need to get additional info now. Are you responsible for the liquor as well? Champagne or prosecco? Mixed drinks? Are there any facilities for food prep on the boat? How long is the party? Do you need to supply tables, chairs, linens, flatware? Do they expect china and glass or paper and plastic? What is their budget?

For 250 people you would normally set up 3 bars and 3 separate serving areas, in addition to the circulating tray staff.

You have 2 main areas to deal with, staff and food. If the caterer was also doing beverages /liquor, that is a 3rd area.

It takes a staff of 10 to set up, serve, and clean up this size party. Usual pay is $100 for 3-4 hours. If the host planned to have wait staff circulate to pass hors douvres, you will need additional staff for that.

If you live in a city with a culinary institute of America school, call them at once, they can help with food and staff.

You need licensed bartenders for each liquor station, they will be harder to find.

You can use your warehouse stores for good food choices, and you can also get restaurants to prep food. Some will even drop off. I need to know where you are and what is accessible.