A nice, easy menu plan. For just 40 people, crock pots will be fine.

I would do this basically as a meal time and a nibble time- mealtime about 12:30 to 2-3; nibbles for the rest, for example, take the crock pots of meat and veggies into the kitchen and just put out some platters of sliced meat, rolls and mustard after 2-3.

Preheat everything on the stove and transfer to the crock pots which have preheated on low with hot water for at least 1/2 hour.

corned beef, start with 1/2 pound raw trimmed brisket per person, cook day ahead (save broth), chill overnight, slice and reheat in some cooking liquid

potatoes, 1 puond per 3
carrots, 1 pound per 4
cabbage, 1 smallish head per 4-6, quartered or sixths
These veggies are cooked in the reserved cooking liquid day of, potatoes in first, then carrots; cabbage only about last 20 minutes.
Have some spicy mustard, 2-3 loaves of rye bread, maybe a couple pounds of sauerkraut, too
shepherds pie, about 2 9x13 dishes- could do 3 if you don't mind leftovers

fruit, do 1/2 the deluxe tropical tray, see fruit tray page,but make 3 small trays out of it and keep the extra trays chilled until they need to go out. Can be prepped day ahead except the berries, which you want to rinse and place day of.
cheese trays, about 4 pounds, some Swiss and some cheddar sliced for sandwiches. Make 2 trays. about 3 pounds of crackers and crunchies. Can be done ahead if wrapped well or purchased pre-sliced and opened to serve.

Texas caviar, 5 -6 quarts
onion dip, 1 cup per 5-6
Chips or other dippers, 3-4 pounds
all these can be done ahead

Sheet cake, full sheet or 2 layer 1/2 sheet serves 50

You might just have these around for after the cake cutting-
cookies, cupcakes; about 2 modest size per person

Consoider dinner coffee, or a couple of drip pots as part of the beverages, it is often relished with cake.