The K cups are interesting, but this is a very awkward and costly plan for 250 people. You need literally gallons of coffee. Renting or buying a 50-60 cup urn for coffee and a 12 cup or 2 for the decaf would likely be less expensive and more effective. You will be making about 3 urns regular for 250 people.

Dinner or reception coffee and tea per 100 Regular coffee, 1 1/2 pounds (about 75 cups)
Decaffeinated 1/2 pound (may use 1 pound regular and 1 pound decaf with older guests)
Additional hot water about 30 servings
PLUS Tea bags(herb, regular, decaf) for 30, 2 pounds sugar, 2 quarts cream or milk, sweeteners, honey

iced tea (sweet and unsweet),
Iced tea or lemonade or fruit punch/koolaid for lunch, per 100
6 to 8 gallons (do 6 with the lemondae
Iced tea is made with 5 ounces or a scant 2 cups loose tea
PLUS ice, sugar, sweetener, lemon or lime slices
Sweet tea drinkers. contains 1 1/2 to 2 cups of sugar per gallon of hot tea Have about 2 gallons unsweetened plus some artificial sweeteners (I like the pink stuff and the green stuff) for sugar free

lemonade, 6 gallons per 100

water, 2 bottles per person, buy where you can return unopened cases