Whisk together buttermilk, hot sauce, salt, smoked paprika, garlic powder, onion powder, and pickle juice if using. Add chicken, coat well, and refrigerate 4 to 24 hours.
Combine crushed cornflakes, flour, cornstarch, salt, pepper, paprika, garlic powder, onion powder, and cayenne in a shallow bowl. Stir well.
Remove chicken from marinade, letting excess drip off. Dredge each piece in the coating, pressing firmly. Dip back into the buttermilk marinade, then coat again in cornflake mixture to build a thick double crust.
Place breaded chicken on a wire rack or parchment-lined tray. Rest at room temperature 15 to 20 minutes to help the coating set and adhere.
Preheat air fryer to 375 degrees F for 3 to 5 minutes. Lightly spray the basket with oil. Arrange chicken in a single layer without crowding. Spray tops generously with oil.
Air fry at 375 degrees F, flipping every 10 to 12 minutes and spraying with oil each time. Cook times: drumsticks and thighs 25 to 30 minutes, leg quarters 30 to 35 minutes, split breasts 30 to 40 minutes. For extra crispy skin, increase to 390 degrees F for the last 3 to 5 minutes.
Sprinkle immediately with finishing salt if desired. Serve hot.