Please keep in mind that "hard-wired" workflow templates are just that: hard-wired. This means that a specific workflow template (for example WS53100044) will always have the same number of steps, each step will always have the same type and number, agents will always be assigned in the same way, and those can't be altered by configurations. To understand each workflow template's behavior, you can either open that template in transaction PFTC or SWDD, or alternatively, read the exact behavior in SAP Help documentation. You basically need to google the workflow template number and you should be able to find the description of each template's behavior (by the way, the number you type has an extra zero so if you can't find a match on Google, you will know why 
).
Now, the assignment of CR steps to CR type is done in the workflow template itself and NOT in the decision table. See the first screenshot:
The step number above "should" correspond to what is in the configuration table (for readability and consistency of documentation purposes). However, if for some reason, it does not, the hard-coded value is the value that will actually be considered. So, in technical terms, the assignment of step numbers in MDGIMG has no influence on how the workflow template will behave. Again, the main purpose is for the corresponding description in the step number configuration table to show on the CR window.
The other thing is the step type. A step type purpose is mainly to indicate what set of buttons will show at the top of the CR window. The fact that step types are represented by numbers confuse a lot of people with step numbers. I would have personally preferred if step types were a 2-char field so that a clear distinction can be made between step types and step numbers. In any case, buttons on the CR correspond to actions and you can see in MDGIMG that you can assign step types to actions. SAP delivers a pre-defined set of step types and associated actions. Those must NOT be altered because they could break the standard workflow templates. However, you can create your own custom step types and link them with as many actions (standard or custom actions) as you like. But again, you can't assign those custom step types to hard-wired workflow templates. You can only use them in your custom workflow templates or in the rule-based workflow.
Now, the question is how does the hard-wired workflow know what step type to use. The answer is easy: you can either find that in the SAP Help documentation or in the workflow template definition in transaction SWDD. For the above screenshot, the step type is 2. You can find that if you double-click the task ID TS75707980 (or display it using transaction PFTC) and look in the "Cntainer" tab. In this case, this task will ALWAYS have type 2. Other tasks are assigned different step types or are more dynamic in the sense that they expect the step type to be passed from the main workflow template calling them. For example TS53200002 will always have type 7, TS60808005 will always have type 5, and TS60807954 accepts the step type dynamically. This last one is the one used in the rule-based workflow (hence it has to read the step type configured in the decision table).
I hope this answers you question. You definitely need some level of workflow design/build knowledge in order to be able to completely understand all of this. Hopefully, this gives you a good starting point.