To prepare stock, combine first 10 ingredients in a large stockpot. Bring to a boil; add turkey breast. Return to a boil; reduce heat, and simmer for 1 1/2 hours or until turkey breast reaches 170° (use an instant-read thermometer). Carefully remove the turkey breast from stock. Cover the turkey breast, and refrigerate. Strain stock through a colander into a large bowl; discard solids, and return stock to pot. Reduce heat, and continue to simmer stock until reduced to 2 quarts (about 1 1/2 hours). Cover and chill stock for 8 hours. Skim solidified fat from surface of stock, if necessary.
Preheat oven to 250°.
To prepare turkey, rub poached turkey breast with oil. Sprinkle with 1/2 teaspoon thyme, 1/4 teaspoon salt, 1/4 teaspoon garlic powder, and 1/4 teaspoon pepper. Wrap the turkey in heavy-duty plastic wrap and foil. (Double-wrapping in plastic and foil helps retain moisture when reheating.) Bake at 250° for 2 hours or until thoroughly heated.
To prepare the stuffing, melt 1/4 cup butter in a large Dutch oven over medium-high heat. Add the diced onion and diced celery; sauté 3 minutes. Stir in bread cubes and the next 7 ingredients (bread cubes through 1/4 teaspoon pepper). Stir in 2 1/2 cups turkey stock. Place in a 13 x 9-inch baking dish. Bake simultaneously with turkey at 250° for 1 hour and 55 minutes.
While the turkey and stuffing cook, prepare gravy. Melt 1/4 cup butter in a large saucepan over medium heat. Stir in flour; reduce heat, and cook 15 minutes or until lightly browned. Gradually add reserved 5 1/2 cups turkey stock, stirring with a whisk until blended. Bring to a boil; reduce heat, and simmer until reduced to 3 cups (about 2 hours).
Uncover turkey; remove turkey breast halves from bone. Slice turkey, and serve with stuffing, gravy, and Vanilla Sweet Potatoes.