step numbers are hard-coded in this workflow template (WS54300003). if you open any task container, you will see the value of the step in the container of that task.
any way, you should not modify workflow WS54300003 as that is considered modification to standard objects. you can copy it to a custom workflow template and then add any new step as you like. you can assign whatever number you like to any step as long as the numbers in the workflow template are consistent with the numbers assigned in the MDGIMG configuration node.
A recommended solution is to use the rule-based workflow template. your MDG process will be much more dynamic and a lot easier to modify/enhance going forward.
this document can help you understand how you can use the rule-based workflow template: How to Fill MDG Rule-Based Workflow Decision Tables