Put buttermilk, 2 tablespoons salt, black pepper, and the hot sauce in a large, airtight container. Add chicken pieces; turn to coat. Cover; refrigerate 20 minutes or overnight.
Buttermilk Herb Mayo:
In a small bowl stir together the mayonnaise with the buttermilk, chives, parsley, thyme, and pepper. Refrigerate until ready to serve.
Put flour, remaining 2 teaspoons salt, cayenne pepper, and baking powder in a large resealable plastic bag.
One at a time, remove chicken from marinade. Place chicken piece in dry mixture bag and shake vigorously to coat. Remove chicken from bag, and shaking off any excess flour mixture, set floured chicken aside. Repeat with remaining chicken.
Line a baking sheet with paper towels.
Attach a deep-frying thermometer to the side of large heavy-bottomed pot or dutch oven, heat oil over medium-high, to 375°F Cook chicken until golden brown on each side, about 3 to 4 minutes a side. Chicken should be opaque in the center. Place cooked chicken on prepared baking sheet to drain.
Dividing evenly spread bottom of buns with: herb mayo, pickle slices, lettuce and chicken, use remaining bun tops to close sandwiches. Serve hot.