This is a very scholarly article but if you really want to understand preexistence then I highly recommend reading this paper by Dustin Smith
John and Jewish Preexistence: An Attempt to Responsibly Set the Christology of the Fourth Gospel in its Proper Historical and Theological Matrix of Thought
And here is Dustin presenting this paper at a 2015 Theological Conference
John and Jewish Preexistence: An Attempt to Responsibly Set the Christology of the Fourth Gospel in its Proper Historical and Theological Matrix of Thought
And here is Dustin presenting this paper at a 2015 Theological Conference