As I don't own an HC-42e I can't say for sure, so your best bet is to RTFM

, but my best guess is as follows:
1. I very much doubt you can set the VF to B&W. On my TRV-900e it is a colour VF and I've never found (or tried) a way to set it to B&W.
2. Manual aperature and shutter speed adjustments allow you more control over the way the picture looks, especially in low light conditions. A slow shutter speed on fast moving images (ie sport) will make the movements jerky. Aperature adjustments allow you to control the depth of field (how much of the picture, foreground to background, is in focus).
Mark.