You want to lift 400 lbs at 20 mph?

If the max lift coefficient is 1.5, you will need 260 sq ft of wing surface. The aspect ratio will largely determine the power required to overcome induced drag. For example, with AR = 5, induced drag at takeoff will be ~40 lbs. You'll need at least that much thrust at 20 mph (not static) if the plane is to climb.