The reason I think the soul is immortal is because the eternal fire that the unsaved end up in is eternal, and the saved have eternal life. The Scripture talking about the eternal flame was in a previous post I had in this thread.
I think the soul consist of emotion, will, intellect. I don't know if scripture entirely backs that up. That is kinda my own speculation.
The Spirit of man is dead, until it is quickened when the person becomes a christian. So the unsaved's spirit is still dead. Therefore man is imcomplete until they become a Christian, our spirit is what communicates with the Holy Spirit. That is taught in the Bible, if you want verses let me know and I'll look them up. Off the top of my head, I think it talks about it somewhere in one of the books of corinthians.