The short answer to this week's topic is- however much the story demands. Paranormal, Fantasy and Science Fiction all require a different kind of world building than other fiction. You create the world your characters inhabit. Either fantastical, futuristic, or simply an otherworld on this plane. Then you populate that world with characters. You give the characters traits and the characters drive the story.
Laurall Hamilton, Charlaine Harris, and Kim Harrison all do this well. In each of these examples, the authors have built worlds with multiple supernatural elements and multiple supernatural characters. As long as the world is developed skillfully, the characters three-demensional, readers will buy what is presented to them. It's your job to make it believable within the walls of the world you've designed.