Your're the first person in years who has mentioned Michael Newton -- I read his Journey of Souls -- amazing book!
I have read Matrix Gold which speaks of simultaneous incarnations -- one Soul who is living out 1,500 - 1,600 lives at once -- each in a different location and time, all of these memories becoming part of the Higher Self (the Soul). When the final incarnation is finished, the Soul and all of its lives depart for another dimension. This book also mentions that our 'helpers', 'guides', etc. are our own higher selves and the Soul's other lives who come to the aid of any part of the Soul when required.
Then, there is the sequential reincarnation where each Soul lives only one life at a time over many eons -- each life, again, adding to the experience of the Soul. When the final incarnation is lived, the Soul departs for another dimension.
I am now fairly certain that there is a magnificent trip ahead for each of us -- we just don't know the whole story and won't until we leave this life. But, just knowing that there is such a trip ahead helps with life here and with any thoughts of what lies beyond.