While there isnt really a minimum, its a good idea to have a choice every two or three pages. You can even flavor this with links to an optional worldbuilding page (like Necromancer) that cuts back to a previous page. A similar thing can be done with dialogue options for having the protagonist learn about the other characters.
Just dont over saturate your story with choices like this otherwise the comments would be flooded with "FAKE CHOICES 1/8"
Unless your storygame is cave of time style, then every choice.is a real one.