In a medium pot, cover the sweet potatoes with water and bring to a boil. Cook until tender, 12 to 15 minutes. Drain and return to the pot. Mash with the buttermilk, chives and hot sauce; season with salt. Cover to keep warm.
While the potatoes are working, heat a large cast-iron skillet over high heat. Rub the steaks evenly with the steak seasoning, chili powder and coffee. Add 1 tablespoon oil to the skillet, 1 turn of the pan, and spread it around with a folded paper towel. Add the steaks and cook, turning once, for 8 minutes. Turn off the heat, tent the skillet with foil and let rest for about 10 minutes, turning once halfway through.
While the meat rests, in a small saucepan, heat the butter until foaming. Stir in the parsley.
In a large skillet, heat the remaining 1 tablespoon oil over medium-high heat until smoking. Add the onion, bell pepper and corn and cook until browned at the edges, about 2 minutes. Stir in the kidney beans and cook until heated through, 2 minutes; season with the thyme, salt and pepper. Slice the steak against the grain and divide into 4 portions. Pour the parsley butter on top. Serve the steak with the succotash and sweet potatoes.