Inspiration of Scripture

It's hard to decide if Paul is meant to be taken as scripture. Yes, he was given a message by the Messiah, the gospel/good news to preach. But are we really supposed to think that every single word he spoke and every bit of advice he gave were specific words directly from the mouth of YHWH Himself?
If the spirit of God gives you a message to tell, does that mean everything you say from that moment on is to be taken as inspired? Does that mean you will never again make a mistake in anything practical or spiritual?
Paul seems to contradict Torah and the Prophets at times. Is this because we don't understand his meaning or did he make a mistake? When he preached, at least once, after people saying 'I follow Paul, I follow Yeshua, I follow Apollo...' he said, "I was determined to know Christ only and him crucified." Is this because people were assuming everything he said had as much authority as that of Messiah himself and he didn't accept that?
Why is it that anyone thinking Paul made a mistake, or was just plain wrong, is considered an evil heretic? Who decided that Paul was another Messiah with perfect wisdom, no longer fallible and human? King David, King Solomon, Jonah, all those "great men" of the Bible were clearly shown to be fallible, sinful - it was their hearts that repented (and often!) that made them great.