Typically just 3 or 4. I also keep the values not too dark or bright at the start, so I keep the value range within 2 to 8 on an 11 step scale. That gives me some wiggle room. Most of the preliminary shapes are made in solid neutral colors with no shading.
One approach often used effectively is to start with a solid single undertone, add another layer of lights and darks with the full range of values, and then apply the color in glazes.
If you work more alla prima style then you can also use a broad value range at the start. It's more a matter of controlling the amount of the pigments and their opacity.