In case you wonder, these will be stories in the coming seasons. There will be other types of stories as well, such as harvesting vis sources or securing some of the resources the covenant lacks. So it is a matter of what kind of story you'd like your magi to be involved in.
In this first cycle, I think each magus should probably be involved in 2 stories -- maybe 3 if they are short enough. That number includes any story in which you pursue personal goals for your magi, or generated by your Story flaws.