who are they and what are their beliefs?
how does the circle of five relate to family, friends, peers and what do they believe
about the world as they see it.
what will their experiences be in the circle and out of it?
what challenges and benefits do they derive out of being a circle of witches?
how did they come about to be the group that they are?
these are possible questions you may want answered in your book.
certainly you can build a life about the circle five.
you might want to know them as a group and individuals for the book.
once you give the characters life, then get to know tham well, so that you can elaborate and embellish them for fiction's sake.
then you can build on answered and unanswered questions as they arise.