Dr. Dierdre Good, professor of New Testament at General Theological Seminary, has posted a useful summary of what the Apostle Paul seems to have know about Jesus. Remember, the undisputed Pauline epistles were written in the 40s and 50s AD, and the first Gospel chronologically was Mark, and not written until the 70s. So Paul didn't have any written traditions about Jesus, just verbal ones. In essence, Paul has the first Gospel, embedded in his letters.
Here's an excerpt from Dr. Good's blog:
Let's take the first question: what does Paul know about Jesus? Paul knows that Jesus descended from David "according to the flesh" (Romans 1:3) so Paul knows that Jesus was Jewish. From the same passage, Paul knows about Jesus' resurrection. Paul's gospel of God describes God's designation of Jesus as Son "in power, according to the spirit of holiness" by his resurrection from the dead (Romans 1:4). As we know, Paul has an encounter with the resurrected Jesus. He describes it in Gal 1: "God was pleased to reveal his Son to (or "in") me so that I might preach him among the Gentiles (1:16).
Read her entire summary here.