I work as a baker in a cafe, but my boss is also a caterer, a good one. Our place did a five hundred person reception for the First Lady Laura Bush, when she was the “star” at our library’s grand reopening.
To get down to nuts and bolts, how much is the friend willing to spend per head of guests? That will give you a figure to start with.
Will it be disposables or china? If the latter, do you own or have available such tableware, or will you have to rent? What about table linens, coffee/tea urns, glassware? Is the affair outside or inside, and what power sources are available? Do you have, or will you need chafing dishes? Will you be able to do all the work yourself, including set up, or will you need to hire help?
I’d look at all the above items to calculate overhead. Then work out two or three menus that fit the given budget. If there’s one thing I have learned about catering, it’s that the customer usually wants lavish presentation at fast food prices. For all the work this is going to entail, don’t sell yourself short. If the friend can’t come up with the bucks, regretfully decline.
Oh, if it is for 18 people, you need that amount of items for each entree, but don’t make them large. And the customer should not count on there being extra food, “just in case” there are more people at the last minute. You need a cutoff time for the exact number, and if you do manage to provide for, say, a nineteenth person, charge for that. Customers sometimes try to be cheap, to have 20 folks, while buying for 18, assuming there will be more food.
If you do set up for, and are paid for 18, then they get the leftovers if they want them. If you have any more questions, shoot me an email.
Remember that reception I helped with for the First Lady? That’s why I hate, absolutely hate making mini-tarts and quiches. Try shaping 1000 of those friggin’ crusts by hand, filling and baking, hour after hour.