If time, marinate the chicken: whisk buttermilk with hot sauce and a pinch of salt. Submerge the chicken thighs and refrigerate for at least 30 minutes, up to 2 hours. This step keeps the meat tender and adds a gentle tang to the crust.
Prepare the coating: in a shallow dish, mix flour with paprika, garlic powder, onion powder, cayenne, salt, and black pepper. This will become the crispy crust that encases the chicken.
Pat the chicken dry and remove excess moisture. Dredge each piece in the flour mixture, pressing gently to help the coating cling.
Heat oil in a deep skillet or Dutch oven to about 350°F (175°C). Fry the chicken in batches, turning once, until the crust is deep golden and the internal temperature reaches 165°F (74°C). This usually takes about 6–8 minutes per batch depending on thickness. Transfer to a rack or paper towels to drain.
Make the slaw: in a bowl, combine shredded cabbage, mayonnaise, apple cider vinegar, sugar, salt, lemon juice, olive oil, and celery seed if using. Toss until the cabbage is evenly coated and slightly softened. Let it rest for at least 10 minutes for the flavors to mingle.
Warm the tortillas: either wrap them in a dry skillet over medium heat for 15–20 seconds per side or warm them in a humid towel to make them pliable.
Assemble: slice the fried chicken into thin strips or bite-sized pieces. Place a few pieces on each tortilla, top with a generous spoonful of slaw, and finish with a squeeze of lime if desired. Serve immediately while the chicken is crisp.