I worked with variations of 10. To make it bigger, just cast on 90. When you increase you should end up with 120. Make the yellow section longer, I would say 4 inches or so. Since the base is ribbing, it should be a good diameter for most people, but you can experiment with the length. I think if the increase were more drastic, for instance K1, K1F&B, the frosting would be more dramatic, but I have not tried it. As long as the numbers of stitches after increasing is divisible by 10, it should turn out fine. Experiment, like when you bake!
Momo