Whisk eggs and sugar in medium saucepan. Whisk in vinegar and 2 tablespoons water. Bring to a boil over medium-high heat; boil 4 minutes or until thickened, stirring constantly. Pour into medium bowl; whisk in mayonnaise, mustard and salt. Refrigerate until well-chilled.
Meanwhile, cook potatoes in large saucepan of simmering water over medium to medium-low heat 20 minutes or until just tender when pierced with a knife. Drain; cool. Peel; cut into 1-inch pieces.
Layer potatoes, celery, red onion, eggs, dressing, green onions and sunflower seeds in large clear bowl.