>>5747053depends. Usually I start with just one layer, then once the polishing, lineart and colours kick in the amount of layers can go through the roof. I usually keep all my colours on a single layer, I don't really see much value in the layer modes like "multiply" that so many people use.
It seriously depends what I'm drawing. In scenes with more than one character each gets at least a single layer for himself. But in things with only one character I might even start and finish on a single layer. I'm used to traditional and also used to draw a little in MS paint, and there you had to get creative how to do both sketch and lineart on the same layer.