I think your requirements are similar to those asked in this forum question.
Yes your thinking is correct as in having an activity that updates an external system responsible for interacting with the human actor, and then use signals to notify the workflow of the completion of the human decision.
Note that with temporal you can write your code to wait for multiple signals, in the case where you might require decisions from multiple human actors in order to move forward with the next activity. This post has some code samples that show off how to do it completely async.
You can think of task queues as “endpoints” on the temporal server. Your workers listen to those endpoints waiting to pick up tasks and use the task info to process /continue processing your workflow executions.
Let us know if you have any further questions / concerns.