My Questions On Contests???

Ive seen many contests hosted by many bloggers, and I have decided that i infact want to do a contest, but i currently only have 14 followers and want to know the perfect time to start doing contests.
I already have some books to give away and would do it now but I know I would have many entired.
So can someone please tell me how many followers after would you decide to do contests?
Thank you