How influential? Very.

13/27 New Testament books are attributed to his authorship, 7 of which modern critical scholarship generally considers to be "authentic", the rest disputable. Even if you reject that other 6, the idea that they were attributed to Paul would reflect the authority and influence he had.

Paul appears to be the prime mover in terms of expanding Christianity from Judea and Syria into Asia Minor, Greece, and beyond, and plays an important role as missionary, establisher of churches, and theologising early Christian belief into a Hellenistic context, which for Western and Orthodox Christianity is the most dominant influence from that time period.

I don't think asking how Paul's teachings differ from Jesus is an easy question to answer, because we don't have any writings from Jesus, and so Jesus' other teachings are mediated through the gospels, which are themselves theologised writings.