Did Paul receive the Gospel from man or not?

Yes
1. "For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, 4and that He was buried, and that He was raised on the third day according to the Scriptures, 5and that He appeared to Cephas, then to the twelve (1 Cor. 15:3-5)."
No
1. "For I would have you know, brethren, that the gospel which was preached by me is not according to man. 12For I neither received it from man, nor was I taught it, but I received it through a revelation of Jesus Christ (Gal. 1:11-12)."

Many have argued that there is a necessary contradiction between 1 Corinthians 15 and Galatians 1. In 1 Corinthians 15, Paul received a creed (formulaic statement of belief) and passed it on to the Corinthians. This creed was probably composed shortly after Jesus' crucifixion by various Christians. Many scholars argue that Paul likely received this creed from the Jerusalem apostles (cf. Gal. 1-2). However, Paul says in Galatians 1:11-12 that he did not receive the Gospel from man.

In response, it is important to note a couple of observations. First, while Paul is passing on a particular formulaic statement of belief in 1 Corinthians 15, the source of that statement of belief is Jesus Christ. Jesus was the ultimate giver and authenticator of the creed. Likewise, Jesus is the ultimate source of Paul's knowledge of the Gospel as in Galatians 1. Therefore, there is no contradiction between the two passages.

Second, in the context of Galatians 1 and 2, Paul visits Jerusalem at least twice (cf. Gal. 1:18-19; 2:1-2ff). In one of these trips, he discusses the content of his Gospel with the Jerusalem apostles such as Peter and James (Gal. 2:1ff). Paul indicates that he questioned and wanted to verify the certainty of his message. Therefore, according to Paul, there was no necessary contradiction between Jesus being the ultimate source of the Gospel whether through a creed or direct revelation.