You should be able to do this all in one microflow.
You can break it up into more than one microflow if you want to (maybe for reusability) and call these as sub-microflows.
One thing to consider is how long the API call will take to execute. This can make your app appear slow to users. In this case, you can put a blocking progress bar in the Microflow settings option of the action button that calls the microflow.
I hope this helps.