Gently dry chicken thighs with paper towels. In large bowl, whisk buttermilk, hot sauce, 1 tsp salt, garlic powder, onion powder, ½ tsp black pepper, smoked paprika.
Add chicken to marinade, toss to coat completely. Cover and refrigerate 1-4 hours (overnight best for flavor).
In shallow dish, combine flour, cornstarch, 1 tsp salt, paprika, cayenne, ½ tsp black pepper for breading.
Remove chicken from marinade (excess drip off). Dredge each piece in breading mixture, pressing firmly to adhere.
Place breaded chicken on wire rack over baking sheet. Rest 20-30 minutes at room temp (helps coating stick).
Heat ½-inch vegetable oil in large cast-iron skillet to 325-350°F. Fry 3-4 thighs at time, 4-5 min per side until deep golden (165°F internal).
Drain on clean wire rack. Sprinkle flaky sea salt while hot. Serve immediately with lemon wedges!