I think it's extremely probable that a 1st Cent. Jewish rabbi named Jesus (or his Aramaic equivalent)actually existed, had a significant following, was considered to be the Messiah by his followers, and most likely was crucified.
If for no other reason than the fact that by the time Paul began his ministry (which may have been as early as 49 BCE.) there was already a well established church based on the afore mentioned beliefs.
If you base calculations for the date of the crucifixion on Josephus' account of the ministry/execution of John the Baptist, then the most likely date is somewhere around 36-37 BCE.
That would mean there was only (at most) a 14 yr. lapse ot time between the end of Jesus' ministry and the beginning of Paul's. That isn't near enough time for a full-fledged religion to evolve out of local legends based on a completely mythical character, especially when you consider that, according to the accounts in Acts and in Paul's epistles, some form of Christianity was already extant and well established by the time Paul showed up.
Taking all that into account the only possible conclusions you can draw about the origins of the Christian church are either;
A. One day around the time the alleged crucifixion was supposed to have taken place, a few people got together and said, "Hey! I'm tired of fishing for a living. What say we start our own religion based on a completely imaginary character that we make up and somehow convince a few thousand local people that he actually existed right here under their noses but somehow escaped everybody's notice".
or..
B. There really was someone named Jesus in 1st. Cent. Judea who's life, ministry, and (probably) death served as a basis for the Jesus that we know.