Your cult author displays his ignorance again and again. Let's start here:
1. The supposed "contradiction" between Saul's conversion accounts in Acts.
As has previously been shown, the word translated heard in both these accounts can mean either heard or understood. These accounts are easily reconciled by showing that those around did not understand the voice, though they heard the sound and recognized it as a voice.
2. The "inconsistency with Timothy" and his instructions to the church in Galatia.
Again, as has been previously shown, Paul instructed the Galatians not to be circumcised because the Jews were saying that they had to in order to be saved. Paul affirmed Jesus' own words that the only requirement for salvation was belief in the only begotten Son of God.
When Paul had Timothy circumcised, he did it not for salvation, but so that Timothy could accompany him on his missionary journey to the Jews. The Bible even tells us this. It was not for Timothy's salvation, and I'm sure Timothy knew that. This is neither inconsistency nor contradiction.
3. The treatment of Paul as ignorant of the Old Testament
Paul was a Pharisee. He learned from Gamaliel, one of the most respected pharisees. In order to be a pharisee, one had to know the Torah, the Prophets, and the Wisdom writings to the point of having most of them memorized. He was not ignorant of Old Testament law, and he was a Jew. If anyone had a reason to boast in their works, it was Paul. But instead he preached the good news of salvation by faith alone. Paul would have learned the writings in their original Hebrew, not in the Greek septuagint. To make the claim that Paul knew only the septuagint puts the author's ignorance on full display.
4. The suggestion that Paul's claim of salvation by faith alone is unscriptural
There are many direct quotes from Jesus that can be used to demonstrate the fallacy of this, but the most commonly known one is this:
"For God so loved the world that He gave His only begotten Son, that whosoever believes in Him should not perish but have everlasting life. For God sent not His Son into the world to condemn the world, but that the world through Him might be saved."
Similarly, there are the words uttered to the thief on the cross - a sinner who repented in what were quite literally the last hours of his life:
"Truly I say to you, today you will be with me in paradise."
According to the law, there is no way that Jesus could say that to the thief. He had no chance to atone for his sins. He had no chance to prove his faith by works. Yet Jesus told him that he would be with Him in paradise that very day.
5. The suggestion that Paul's usage of the phrase "there is none righteous" is wrong.
Jesus Himself said "Why do you call me good? There is none good but God." He also demonstrated, as is affirmed by James and Paul, that whoever breaks even one little part of the law is a sinner and guilty of all of it. The only righteousness any of us have is the righteousness of Christ.
This list could go on and on, with plenty of scriptural and contextual rebuttals. Your author, like you, starts with the premise that Paul is wrong - and why? Because he wants to be one of the "righteous" and wants people who don't agree with him to be numbered among the "wicked." And he wants to be able to prove his "righteousness" by his works, and the "wickedness" of others by their lack thereof or merely their disagreement with him.