Go to the local library and find the older issues of Taste of Home. There used to be a section called cooking for a crowd or something with the word crowd in it. Often it had charts and grafts for amounts of food to cook for X amount of people, like for something like meatballs it takes 1/4-1/2 lb. of hamburger meat per person......it is also full of ideas of foods to fix that are for large groups. Most of my dinners at church have been for over 100 and I almost always use Taste of Home recipes.
Some of my fav's have come straight from their pages. There are also many recipes in other magazines and some publications just for large quantities of food for large crowds.
I have cooked 5 onion soup for 125, spinach salad , orange glazed carrots, or steamed mixed squashes, and the meat was a flattened pork loin. We flattened it and put cornbread stuffing from Pepperidge farms inside. We used twine to tie it shut for cooking. The meat was pretty and wonderfully tasty. We sliced the meat across the short way and gave several slices to each person. They reminded me of pinwheel tortilla roll ups. We just baked them until they were not pink inside. This is one of my favorite Christmas meals for a crowd.
One of my favorite meals is Lion House Sweet and Sour Meatballs served over/with oven steamed rice, veggies, and a salad.
I even did Chicken Parmesan. I dredged the flattened chicken breasts in a flour seasoning mix, then fried them up, placed them in large cookie sheets in a low tempreature oven to keep them warm, made gallons of marinara sauce, sliced the mozz. cheese myself. I did place the meat on a bed of cooked spaghetti, cooked some green beans with butter and garlic powder on them for the side, added a salad with Italian dressing and done. It was one of the prettiest dishes I had ever put together. The white pasta with the golden brown chicken, the red marinara sauce with a slice of white cheese to top it off was really pretty then add the bright green.
There are many ways to approach what to do. Are you having light hors de'ouvers snacks or appetizers then a sit down dinner? Is it going to be paper plate friendly or actual dishes with much clean up afterwards, is it all hot food or all cold? A mix? You have a lot to decide even before considering a caterer. Go to the local library and check out some books on entertaining or setting up a buffet. There are tons of books that will help you define what you want.