Your definition of what an apostle is (“In the early church an apostle had to have been taught directly by the Lord, and had to have personally seen Him in a post resurrection appearance.”) seems to say that Paul is not an apostle. Am I right with my understanding of your statement? If I am right, how is it then that Paul defend very much his apostleship?
In 1 Cor. 15:7-8 Paul confirmed that Jesus had appeared to him in a post-resurrection appearance, referring to the Damascus Road event. And in Galatians 1:11-12 he told how he received the gospel he preached directly from Jesus. These events in his life qualified him to be an apostle.