I believe Jesus was a real man for these reasons;
1. The Bethlehem problem.
Normally this is cited as an example of his non-existance, but for me it is the opposite. Here, a 9 month pregnant woman is described as making a 130 mile journey from Galilee to Bethlehem in Judea, a journey which would have caused her to lose the baby.
I don't believe that the story is true, it is there to show the Messiahship of Jesus, as prophecy dictates the Messiah will be born in Bethlehem.
The fact that someone created such a ludicrous story in order to have a man from Galilee have his birth in Bethlehem, to me, suggests that he really did live in Galilee and that this was an important obstacle to his being the Messiah.
2. The Origin of the Apostles
The origin of important characters like Peter and John is clearly given in the gospels, we are told how and where they became apostles. Yet Judas and Mary Magdalene have no origin story, yet play equally important roles. We know that Judas came from Kerioth and Mary from Magdala - but when did they meet Jesus, how and where?
This lack of background suggests to me that the writers of the gospels knew of their existance as apostles, but had no knowledge of their history. A fictional character could easily have been given a brief history.
3. Mary Magdalene
She is an ever present character in the gospels, often taking on the roles of a wife (annointing the body), yet she is downplayed in the gospel narratives to the point of her being declared a prostitute by Pope Gregory I. Why include such a character? Her role could have been played by the Virgin Mary or by Mary of Bethany. She seems unnecessary - unless of course she was a real person.
4. Pre-gospel relationships.
Judas, Mary Magdalene, his brothers and sisters, the family of Lazarus; all examples of relationships which appear to have been formed prior to the gospel accounts. Particularly important is Lazarus as a strong relationship is implied "the one you love is ill" yet such a relationship is unnecessary to the story of the gospel, in fact it only creates confusion whereas a fictional man's life could have been written without any confusion.
5. The Embarrassing Aspects
Peter denying Jesus, the disciples fleeing and hiding rather than protecting the Master, would a fictional account have included such events?
6. The Mandaens
The Mandaens recognise John the Baptist as the Messiah. Yet they also recognise a man named Jesus as existing, but that he was evil and concorted the teachings of the baptist. They could deny his existance, it would make things easier, but they don't.
I believe he was a real man. But i don't believe he was the literal son of God, i don't believe he would of warrented any more attention than any other wandering preacher at the time. His message has survived though, which is testament to the power of that message, the other preachers have fallen into complete obscurity.
Why didn't he write anything down?
Why would he?
The factors which contributed to his understanding of reality, the people and belief systems which allowed him to become what he was existed at his time. People simply had to retrace his footsteps to reach his level of understanding.
Also a teacher of his kind, the type that wanders from place to place, generally has a scribe as one of his disciples. The teacher is asked questions and gives answers, the scribe records these. Look at the Gospel of Thomas for a literal example.
Just like Buddha, it was his followers that were concerned with recording his teachings, the Master simply gives answers to questions posed - usually answers specifically tailored for the person who posed the question. I don't think it was ever his intention to found a religion.
