In cold weather people tend to eat more and in hot weather drink more. The size of side dishes does not need to be the same. For example, when preparing three salads for a crowd of 225 people prepare black bean salad for 50, rice salad for 75 and potato salad for 100. The thinking is that more people would be likely to take potato salad. When increasing a standard favorite recipe to quantity, the rule is never double the seasoning.
Many good books exist with help in quantity cooking.
Carefully mix in remaining ingredients to avoid mashing potatoes. Keep thoroughly chilled until serving. Drain thoroughly and cool slightly. Add the rest of the ingredients and mix gently. Let marinate several hours before serving.