I think that you will find that the vast majority of Wiccans are content with the scientific explanation of how the Universe came to be including the Big Bang Theory and the Theory of Evolution.
That is not to say that that excludes the very real possibility that there was a Divine purpose in setting the natural processes in order. Wicca is not a religion that makes a division between science and religion. Both can exist as complimentary explanations as to how we came to be. This viewpoint is known theologically as Process Theology.
myself i've never heard a Wiccan/Witch creation myth. i believe in evolution. as for the deities, they seem to me less hands on and more observant. they will help us if asked, but won't interfere because they're bored or something. but i don't know the majority's belief. i watched a documentary on tv once about Wicca, this one spoke of 3 different groups, the first group worshiped the Lord and Lady. the second worshiped a gender neutral ball of energy that acted as a god. the third didn't believe there is a god, but rather, nature and ourselves are to be worshiped. right their, three different beliefs, all three believed in the rule of three and karma, they all celebrated sabbats, they followed every last piece of Wicca exactly but when it came to the divine, it differed. i say make up your own belief, research and see for yourself.