@Disillusioned:
There is a difference between theology (Bart Ehrman and co) and archeology (a good primer would be The Oxford Handbook of Early Christian Archaeology).
The archeological evidence for a Jesus or a Paul is very scant, no graves, no contemporary accounts at the time, no records. This indicates their existence was already a myth by the time it was written down.
According to the The International Standard Bible Encyclopedia, Paul's own conversion was dated to be ~31CE based on the writings, that would put it 3 years before Jesus died if you accept 1CE as the year of his birth. Now most scholars and even the Church now date Jesus' birth to ~3 BCE just to keep everything in line, but there is a lot of compression going on.
Basically the entire story of Christ and the expansion of the religion to all of Rome has to fit between ~1CE and 70CE with mass-conversion for the stories to make sense. However archeologically speaking, there is simply no evidence of a widespread mass-conversion.
Most scholars therefore now believe that Christianity was an offspring of Judaism that after the loss of autonomy to the Romans concocted the messiah stories to fill in the gaps of basically where God went and eventually included stories why he allowed the temple to be destroyed. It is believed that the first Jewish rebellions Roman fought (4BCE, when they massacred 2000 messianic Jews) was basically the same group that eventually called themselves Christians.