One roaster serves about 60 people.
Two electric roasters will blow a standard 15 amp electric circuit, which means if you need more than one, you will be plugging them in in different rooms.
It you have a nice big oven, you can use 2 racks and 2 giant turkey roasting pans in the oven. If you use aluminum foil pans you MUST put each on a sturdy cookie sheet. You risk hot food all over the floor if you dont.

A large refrigerated pan takes an extra hour to heat. Use an instant read thermometer to check for 165 n the middle of the casserole.

The biggest risk for food safety is failing to chill fast when making, must go in the fridge asap and be below 40 in 2 hours.

Consider adding some non hot carbs, such as pasta and/or potato salad, marinated bean salad. Then one roaster each of the mostaciolli and potatoes would hold you.