You think Paul was made up?

I think you're going to struggle to find any primary sources to support his existence. Even the Gospel of Mark is dated at around 70 AD, a solid 30+ years after the events it proposes to document. The Epistles all date to 175-400 AD.

Again, imagine if the only surviving copy of the US Constitution we had was composed under the Kennedy Administration.

The common assumption around the New Testament is that it was an oral tradition for at least a generation, and probably far longer. That's plenty of time for a story to shift and spread. Was Paul an original Apostle of Jesus or was he an Evangelical living a 50 years later who had just appropriated the original Gospel messages? Was this a real person or a pen-name? One guy or a cult-branch of the new faith? A church leader who had people working on his behalf? A legacy heir writing on behalf of an elderly/deceased apostle father? A Roman convert using the name of an Apostle to engage in theological debate without exposing his identity to hostile state government?

Its all purely up for speculation.