Combine the flour, 1 teaspoon smoked paprika, seasoned salt, and 1/2 teaspoon black pepper in a large, resealable plastic bag. Add the beef, and seal the bag. Shake the bag thoroughly to coat the beef with seasoned flour.
Heat the olive oil in a large skillet over medium-high heat. Shake the excess seasoning off the beef, then stir the beef into the hot skillet with the onion and mushrooms. Cook and stir until the beef is evenly browned and no longer pink. Drain and discard any excess grease.
Place the beef mixture into a slow cooker. Place the potatoes, carrots, celery, garlic, Marsala wine, and Worcestershire sauce into the cooker with the beef mixture. Pour the beef broth and tomatoes into the cooker, and stir in the onion soup mix and 1 more teaspoon of smoked paprika. Cook on High for 4 to 6 hours, or on Low for 10 to 12 hours. Season to taste with salt and black pepper.
For a thicker stew, combine cornstarch and water in a small bowl. Gradually stir the mixture into the stew until thickened.