Have you considered scalloped potatoes instead, less labor, VERY popular, and the men will eat less meatloaf. Also, no gravy, a real plus with this many folks. 50 pounds raw potatoes per 100.

The freeezable holdable mashed potatoes on this site can be made ahead.

Meatloaf is ground meat, so you must be cautious in both cooking and holding:

.CCP: Cook until internal temperature is 165°F. or higher for 15 seconds. CCP: Hold at 140°F. or higher. Be sure to let meatloaves stand at least 20 minutes before slicing.

A standard recipe for 100 makes 8 loaves in 4 steam table pans. Uses 30 pounds lean ground beef, 1 gallon bread crumbs (3 3/4 pounds), 2 dozen eggs, 12 cups liquid (can be milk, veg /tomato juice, water) and 3-4 pounds minced veg (onions, celery, bell pepper), salt and pepper to taste. You might consider paying the extra for gluten-free crumbs, as a surprising number of people are on gluten free diets these days.

You can use up to 1/3 ground turkey.

Mix very lightly- heavy mixing makes tough meatloaf. 1 hour 15 minutes at 350, regular ovens.

This is a small work staff for this size party. Can you get some help to set up and clean up?