Dressing
2 quarts plus 1 cup mayonnaise- may use 1/3 part plain yogurt or sour cream
1 to 1 1/2 cups sugar
OR 1/2 cup granulated fructose
1 tablespoon fresh dill (not traditional, but good)
Salad:
3 1/4 heads (40 ounces) iceberg lettuce, washed and chopped
6-7 cups crisp real bacon bits, home prepared or bottled
8 medium bell peppers, seeded and chopped
7 (2 pounds) small onions, shredded, chopped fine
OR equal weight green onions with tops, chopped
4 pounds fresh peas or 5 12 ounce packages frozen peas (will thaw in refrigerator overnight)
2 1/4 pounds celery ribs, strings off, cut across ribs into thin crescents
2 pounds carrots, peeled and coarsely shredded
7 cups (1 3/4 pound) shredded cheddar cheese
OPTIONAL 6 to 7 cups croutons, added just before serving

Make the dressing by mixing the mayonaisse and sugar. The day before serving, arrange lettuce in the bottom of deep baking dishes or plastic containers with a cover. Sprinkle on the bacon pieces. Layer each of the remaining vegetables, breaking the peas apart if frozen, then layer in the cheese. Spread dressing over the top of the salad so it is air tight. Cover and refrigerate until serving time.

Normally, the quantities listed first make a salad for 1 person, it is a plateful. When you are serving the Greek Salad with other salads, and it is basically a side salad, you use less.
I have multiplied out for you, giving amounts in parentheses for your shopping list. The larger amount serves about 130 as part of a salad selection, about 100 as main side salad, about 75 as a main dish.

Most often this salad is traditionally served without lettuce, but if lettuce is used, you would use crunchy romaine. If using lettuce, add and toss it with the marinated base just before serving- 1 cup lettuce for a single serving, about 9 pounds for the larger amount.

SALAD BASE

3 ounces cucumber (15 pounds)
3 ounces ripe tomatoes (15 pounds)
2 ounces feta cheese, crumbled or cubed (10 pounds)
1 ounce bell pepper (5 pounds)
1 ounce red onion rings (5 pounds)
1 ounce olives (about 10), PITTED for party purposes (5 pounds)
Greek marinade/ dressing, full recipe
OPTIONAL ADDITIONS at time of service
sprinkling of capers (5-6 cups)
few artichoke hearts (12 pounds)
spoonful of garbanzo beans (5 pounds cooked)
sweet banana pepper rings or pepperoncini or roasted peppers (6 pounds)
If adding celery rings, add about the same weight as onions
1 cup chopped romaine (9 pounds)

Mix the base, bag into zipper baggies, add well-mixed Greek dressing. Refrigerate, turning the bags occasionally to even out the dressing. Just before serving, mix well, stir in lettuce, if added, and sprinkle on other optional additions.

A Simple Greek Dressing/ Marinade

1 ounce olive oil (use at least half real olive oil, please) (6 pints or 12 cups)
1 tablespoon lemon juice (6 cups)
3-4 tablespoons each oregano, garlic, etc to taste
(Lisa's recipe below looks fine, just do upgrade to olive oil)
Salt, pepper to taste

An Oniony Greek Salad Dressing/ Marinade

15 Cups Salad Oil (please use at least 1/2 olive oil)
7½ Cups lemon juice or Vinegar
10 Cups finely chopped onion
3 tablespoons Salt
3 tablespoons Minced Garlic
20 Tsp Crushed Peppercorns
3 tablespoons Rosemary leaves
3 tablespoons Basil Leaves, dried, OR 1/2 cup fresh chopped 3 tablespoons Oregano Leaves

Combine dressing ingredients, shake/mix well, and pour over salad mix. Let stand for 24 hours; will hold up to two days.