You can use between 8 and 10 ounces of dried spaghetti noodles. 8 ounces will serve about 6-8 people, 12 ounces will serve about 10-12.
You can add between 1/3 and 2/3 cup mayo for this dressing. The more mayo, the creamier it will be. I usually use 1/3 cup reduced fat mayo.