Was he viewed as an apostate by the Pharasees and religious leaders?
Yeah, pretty much EVERY GROUP in power in Palestine was his enemy: he pissed the Pharisees AND Saduccees off.
The Torah prohibits the formation of splinter groups/sects from Judaism, making it a death penalty offense. Remember, Paul was born into a Pharisee family, abd he hunted the early Christians down as part of his obligation as an onservant Jew before encountering the vision of Jesus on the road to Damascus.
Reza Aslan has written an easy read on the topic called "Zealot"; it covers the apostasy of Jesus from mainstream Judaism.
Did this lead to his death or was it blaspheming, or are these the same things?
Jesus was executed by the Romans for sedition: by claiming to be the Jewish Messiah ("King of the Jews"), Jesus was directly giving the bird to Caesar, since Caesar was in control of the land of Palestine (an area occupied and under the control of the Roman Empire). That's why simply saying you were the Jewish messiah was an act of sedition, punishable by death by crucifixion, reserved as a form of punishment for crimes against the Empire. The blasphemy charge is NOT consistent with being executed by crucifixion, and the Sanhedrin didn't even have the authority by the Romans to exercise capital punishment of fellow Jews, and they would execute Jesus for a religious sin like 'blasphemy'.
Aslan's a good read: you'd like it, as it's very accessible, factually-correct and meticulously researched with footnotes.
EDIT:
Let me clarify. I have strong doubts Jesus even existed at all, but wondering from the point of view of people interpretting the bible as real events.
Yeah, I don't doubt a Jewish messiah claimaint named Jesus actually lived, and is the kernel of truth upon which the legend of Jesus is based (I'm an atheist, although the real Jesus wouldn't necessarily bear any resemblance to the stories which blossomed in his wake, and grew up around him).
Adam