Bring potatoes to a boil in large pot of cold water that's been liberally salted. Reduce the heat to medium high or a lightly rolling boil and cook for 15 minutes or until the potatoes are easily pierced with a pairing knife. Drain and let cool until just able to handle.
Peel the skins from the potatoes and cut into large diced pieces. Transfer the warm potatoes to a large mixing bowl. Allow the potatoes to cool, about 15 minutes. Add the celery, diced pickles and green onions. Chop 4 of the hard boiled eggs and add to the potato mixture.
In a medium bowl, mix the mayonnaise, mustard, and salt and pepper. Mix well into the potato mixture and season with more salt and pepper if needed. Slice the last egg into thin slices and place the slices on top of the salad. Sprinkle with paprika if desired. Chill for at least 1 hour or overnight before serving.