I intend to write each of the prequel novels just as I did New Spring: The Novel, in such a way that someone could pick any one of them up and begin there with no other exposure to The Wheel of Time, but for best effect, I suggest reading them in the order that they will be published. If you read the second one first, you might find a few surprises spoiled in New Spring: The Novel. And if you read the third one first, you would certainly find spoilers for the first book and some for the second. As for whether to begin with the prequel novels or with the main sequence books, you can do either.