Most of them start in black and white. (cept the two nudes) To color them I follow the follow steps 1: give the whole thing a monotone or duotone using overlay/hard light whatever PS function 2:manually add colors with a color layer. 3: opaque paint
I see these a one shot thing. Focus and try to get everything right in one go. If it fails you start over. There's 10x as much failed sketches. I'd fill 2 A4, 192 page sketchbook per month, on top of school work and making a character design portfolio.
