I've only cooked for a really big crowd (a hundred people or more) a few times, but I've learned the hard way that one of the keys to success has less to do with the cooking techniques and more to do with the tableware and the attitude. Think big and gather up all your confidence. Ask for help.
This is how I ended up serving a salad for 150 people out of a giant washtub usually reserved for the booze at our parties. Here's the story of how the salad came together, if we kept our cool, and the recipe reduced to a more manageable size. More