Fish Taco Platter

Name: Fish Taco Platter
Ingredients: 1 red onion (about 12 ounces), halved lengthwise, cut thinly crosswise; 5 whole small jalapeños; 2 cups seasoned rice vinegar; 3 tablespoons fresh lime juice; 1 tablespoon coarse kosher salt; 1/2 cup mayonnaise; 1/2 cup sour cream; 2 tablespoons fresh lime juice; 1 teaspoon (packed) finely grated lime peel; pinch of salt; 12 ounces tomatillos,* husked, stemmed, divided; 4 green onions, white and green parts separated; 1 jalapeño chile; 2 garlic cloves, unpeeled; 1 1/4 cups (packed) fresh cilantro leaves; 1 tablespoon (or more) fresh lime juice; 2 cups buttermilk; 1/2 cup chopped fresh cilantro; 3 tablespoons hot pepper sauce 3 teaspoons coarse kosher salt, divided; 1 tablespoon fresh lime juice; 2 pounds skinless halibut, sea bass, or striped bass fillets, cut into 1/2x1/2-inch strips; 16 corn tortillas; 2 cups self-rising flour; Vegetable oil (for frying); Fresh Salsa; Guacamole