In a large bowl, combine the buttermilk and hot sauce. Add the chicken thighs, ensuring they are fully submerged. Cover and refrigerate for at least 2 hours, or overnight for best flavor.
In another bowl, mix together the flour, paprika, garlic powder, onion powder, cayenne pepper, salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off. Dredge each piece in the seasoned flour, pressing lightly to adhere. Shake off any excess flour.
In a large skillet, heat the vegetable oil over medium-high heat. Once hot, carefully add the chicken pieces, cooking in batches if necessary to avoid overcrowding. Fry for about 5-7 minutes per side, or until golden brown and cooked through.
Transfer the fried chicken to a paper towel-lined plate to drain excess oil.
To assemble the sandwiches, place a piece of fried chicken on each bun. Top with pickles and coleslaw if desired. Drizzle with extra hot sauce for added heat.
Serve immediately and enjoy your Nashville hot chicken sandwiches!