Bart D. Ehrman's "The New Testament A Historical Introduction to the Early Christian Writings" is an excellent source for addressing this problem and just about anything else about Early Christianity. I don't think he goes into the whole myriad of mystery religions of the period enough; but, that is a huge topic.
Ehrman essentially states that it is not improbable and fairly reasonable to believe there was a 1st century apocalyptic preacher named Jesus who was executed. The majority of the stories about him are probably myths. The parable of the Mustard Seed is the most consistently represented saying of Jesus; so, it is likely that the parable was one of Jesus' teachings.
Ancient History is made up of many stories which probably are not true; but, are not harmful to our overall understanding of ancient life. There is no serious problem with accepting Jesus as a probable historical figure. But, to Bet Your Life and Salvation on such a sketchy story is pretty silly.
If he existed, the Apocalptic Preacher Jesus was basically a Chicken Little philosopher and did not teach the salvation theology of later Christians. He was an End of The World preacher...and he was wrong. It seems life did end prematurely for him; but, the world went on without suffering the cataclysm he predicted.
Actually, the Josephus quote is not widely accepted as authentic. Whatever Josephus wrote was modified by Christian scribes.
Awesome posts guys.....I have enjoyed reading these very much!! This is why I am convinced atheists are atheists, because they understand how the bible was written and the amount of fact there actually is in it. Bloody good work!!