Nori Stacks with Smoked Salmon

Name: Nori Stacks with Smoked Salmon
Ingredients: 1 1/2 cups sushi rice; 3 tablespoons rice wine vinegar; 2 teaspoons sugar; 2 teaspoons mirin (Japanese rice wine); 2 teaspoons sake or water; 1 1/2 teaspoons kosher salt; 4 7 1/2 x 8-inch nori sheets; 1 1/2 teaspoons wasabi paste or 2 teaspoons wasabi powder combined with; 1 teaspoon water; 8 ounces thinly sliced smoked salmon; 1 ounce pickled ginger, cut into narrow strips; 1 ounce prepared wasabi caviar, golden caviar, or salmon roe; Scallion Soy Dipping Sauce