On a web application what should be in tab order?

I see a lot of articles which guide us how to put something in or out of tab order. However, I see no guide on what should be put in tab order.

For example, one of our web app is a list of tasks to perform. On top left corner it shows the overall progress. We have included the tasks in tab order but have left out the overall progress. We have marked overall progress as live region as it is like status and has no actionable item.

However, our QE is of the opinion that that should too fall under tab order. In fact sometimes some people even argue that each head or paragraph tags too should be in tab order.

Where and how do we draw the line?