Re: White areas on canvas
It's a personal choice about your piece. The only suggestion I would have is if there is a lot of white space, just be careful handling it. If the ground is a gesso, it will be absorbant and pick up grease/dirt from hands.
I know a lot of people water-down a neutral tone of paint and lay it down before they start, and then wipe a lot of it off. I know one art teacher that teaches his students to put neon orange or neon magenta--I think this is a bit extreme, and if it shows through, will be way more distracting than white.