The more dishes you add, the less of any one particular food you will need, many people will take a smaller portion of each item, many intending to 'taste' everything, others will be less likely to try every variety of salad etc. Dishes that people can serve themselves easily with a spoon or fork, whether main dish, salad or even dessert are best suited to a Buffet, use tongs to serve a tossed salad, not two spoons, people will be unable to use them with a plate in one hand. Special treats, like baked salmon, shrimp or seafood in a casserole, and 'real' sliced turkey are popular, as well as ethnic specialties that are suited to a particular crowd. Hot roast beef is a treat, but cold slice beef and ham are always acceptable. Add some hot casseroles if you have the oven space, if not add some meat or seafood salads for a large crowd.
Desserts can be sheet cakes, cheese cakes, trifles, fruit platters, cookies and squares.
I would also use cakes etc. The larger the crowd, the simpler things should be kept, as you will find it a 'challenge' dealing with massive amounts of food.