There is no limit to how many Steps you can add to a Topic. However, when a Topic loads, all Steps within the Topic are loaded behind the scenes, so we find that a maximum of 8-10 Steps is a good rule of thumb.
If you find yourself having dozens of smaller Steps, consider either consolidating them into a single Step that encompasses the activity, or breaking your material up into multiple Topics or Subjects.
Steps are a great way to walk through a sequence or process.
You can also add a step in outline view like shown in the below image:
Once completed, Steps cannot be uncompleted by a user.