simple stepper speed control

huh, this isn't playing out the way I thought it would. I have some fuzzy psuedo code that will not work well as the lowest speed stepper gets odd step speeds, bad plan on my part. I am trying to start over, but am stuck in my old ideas. How can I control multiple motors with a single timer?

I am writing code that will use 1 timer per motor, but as I said, that is a huge waste and I might as welll jsut use the Tone library. I need something that works NOW, but want very much to completly re-write it with something better when I have a better idea.