I agree with micadeolu; I believe that his name was changed when in Rome. The Hebrew meaning of the name "Saul" means "desired", which raises the question, "Was his name predestined before his birth?" I believe so. In other words, God desired Saul/Paul to be the leader of the Gentile nations concerning salvation in Yeshua/Jesus Christ.
As far as tithing being a "Christian" practice? No.
It was a Jewish OLD TESTAMENT practice. It was used as a type and shadow of the new covenant. Jesus Christ is our first fruit (tithe) now!