Fresh watermelon slices (for 200)
Assorted cheese and crackers (for 225)
Crackers with strawberry butter (for 200)
Corn cobettes (for 225)
Mac n' Cheese (for 200)
Southern Style Baked Beans (for 225)
Potato Salad (for 125?)
3 or 4 Bean Salad (for 125?)
Apple Cole Slaw (for 100?)
Caesar Salad (for 200?)
Sauteed Burgundy Mushrooms (for the steaks)
Lemon Bars (for 125?)
Chocolate Brownies (for 125?)

The salads can be made up ahead but I don't know when to start the corn.

Also, I was hoping to use the box (large elbow) Kraft mac n' cheese and build on it. Do you have any suggestions as to what to add to make it more unique? Bread crumbs on the top? What about other cheese?

I will only have to use the stove top for the mushrooms and the corn. And I'll only use the oven for the mac n' cheese and the beans.

Assorted cheese and crackers (for 225)
Crackers with strawberry butter (for 200)
15 pounds crackers
20 pounds cheese and butter spreads, logs, slices, cubes

Sauteed Burgundy Mushrooms (for the steaks)
tough estimate- see this recipe:
thepioneerwoman.com/cooking/2010/03/steak-with-burgundy-mushroom-sauce/
She uses 1 pound mushrooms per 4 servings, and you are talking 200...

Corn cobettes (for 225)- 1 per person

Mac n' Cheese (for 200)- 1 pound pasta per 10, 1 quart white sauce per pound, 1/2 to 1 pound cheese per pound. You don't need the box; see my classic mac and cheese or my bargain mac and cheese on the Big Pots page. I dust the pans w/ Parm after greasing/buttering, and throw in about 1/4 cup Parm with the melting cheeses, for flavor and salt. You cqan even do French fried onions (the same ones used for green bean casseroles) for topping- tasty.
Be aware that you are looking at around 10 gallons- 2 to 3 electric roasters- way more than 1 oven can hold

Southern Style Baked Beans (for 225)- 18 pounds dry beans. Make some meatless. You want to end up with 3 gallons per 100

Potato Salad (for 125?)- nope, everyone takes some; at least 70 pounds of potatoes, for at least 7 gallons
3 or 4 Bean Salad - 4 to 5 gallons
Apple Cole Slaw (for 100?)- 4 to 5 gallons
Caesar Salad (for 200?) - yes, use the paln for 100 table for amounts and dressing amounts

Lemon Bars (for 125?)
Chocolate Brownies (for 125?)
do small bars; 3 lemon per each 2 people, 2 brownies per person, make some nut free
Fresh watermelon slices; (for 200)- 1/2 pound whole per person, ice it

Barely cook them- just thawed and heat through thoroughly- before transferring to the chests.