Place the chicken in a large airtight container. Mix the buttermilk, 2 tablespoons of the salt, and the sugar in a medium bowl until the salt and sugar dissolve. Pour the mixture over the chicken, add the herbs (if using), cover, and refrigerate 6 hours or overnight.
Stir together the paprika, black pepper, the remaining 2 teaspoons salt, the garlic powder, and the cayenne in a small bowl. Combine the flour and baking powder in a 1-gallon resealable plastic bag or a large lidded container. Seal the bag (or cover the container) and shake to combine.
Drain the chicken in a colander (discard the buttermilk) and transfer to a baking sheet. Sprinkle the chicken with the spice blend. Add 1 piece of chicken to the flour mixture, seal the bag, and shake to coat. Transfer to a plate and repeat.
Pour enough oil to fill a 12-inch heavy-bottomed skillet to a ½-inch depth. Heat the oil until it reads 325°F to 350°F on an instant-read thermometer. Carefully place the chicken thighs in the center of the skillet (because they take the longest to cook) and the legs, breasts, and wings around the perimeter, being careful not to overcrowd the pan. (You may have to fry the chicken in batches.) Fry until the chicken is golden brown and crisp on both sides, and an instant-read thermometer inserted into the chicken reads 165°F for the breasts and 170°F for the drumsticks and thighs. Transfer the chicken to a wire rack and let cool slightly before serving.