Four things I would do in setting up with a featureless white backgound, like in your sample shot:
1-As much physical separation as you can between subject and background. 8, 10, 12, even 15 feet.
2-Set exposure for the face using spot metering on the face.
3-Light your background for over exposure, i.e. pure white is the target
4-Take your F5 and get behind your subject, without shadowing the subject and verify that the light bouncing back toward the camera at the subject is less than what you are setting your big camera at. This keeps you from getting a halo effect.
The other scenario you pose is simply a normal exposure shot where you put the subject and background in their proper "zone". i.e. the Blonde in 6, everthing else in say 7, & 8. You might lean toward overexposure a bit for effect.
In Low key the Blond is still in 6 or maybe even 5 or 4 for effect, the rest would be in 4, 3, 2, even 1