Length of a series.

I'm currently working on a story that came to me in a dream. The piece however has quite a large amount of potential and myself being a relatively new writer was wondering what fellow writers think the length should be. The story is about a world in between life and death where a group of people are out on a goal to revive someone close to them. Given this info which of the following lengths (which I chose for a reason) should be used? I would also like to say thank you for your time.