Here's how I would start: Convert the image to CMYK. Invert the image. Split channels, print and label the negatives. Start with the Cyan, then Magenta then Yellow then Black. Unless you have a totally mechanized approach, your development will require some observation to determine when a particular layer has cleared. This would be difficult to do if black were your first layer. Many gumprinters never use black (and the forums would get heated at times regarding this). I DO use black, but I always put in on last, because this allows me more control.