Cook pasta in salted water to al dente. Drain and rinse under cold water until fully cooled. Drain very well.
Hard-boil eggs: cover eggs with cold water, bring to a boil, turn off heat, cover, and let sit 10–12 minutes. Transfer to an ice bath for 10 minutes.
Peel eggs. Slice in half and reserve two yolks. Chop remaining eggs.
In a large bowl, whisk mayo, sour cream, mustard, relish, vinegar, sugar (if using), salt, pepper, and paprika. Mash reserved yolks into the dressing until smooth.
Add pasta and toss until coated. Fold in chopped eggs, celery, onion (if using), and herbs (if using).
Cover and chill at least 1 hour. Stir before serving and adjust seasoning. Sprinkle paprika on top.