Had Paul written any epistles before the Jerusalem council or was he only seeing Gentiles saved?
No. During the eleven years from Paul's Gentile ministry in Tarsus until the Jerusalem council, he had not yet written any epistles. He was, however, seeing Gentiles brought into the body of Christ. His first written letters were the Thessalonian epistles, around AD 54.
Les explains that after Paul's three years of instruction from God's personal seminary, Paul went to Tarsus around 37–40 and began his work among the Gentiles, always approaching the Jew first. By Acts 15, the Jerusalem council, the Jews were calling him on the carpet for going to Gentiles. Les points out the time interval: from the start of Paul's Gentile ministry in Tarsus until that council was already eleven years. During that eleven-year period, Paul still had not written any epistles, but he had been seeing Gentiles brought into the body of Christ. Les then notes the dates of the letters: the Thessalonian letters were first, about AD 54; Galatians about 58; 1 Corinthians 59; 2 Corinthians about 60; Romans the same year; and later, from Rome under house arrest, Ephesians, Philippians, Colossians, and Philemon. By the time he wrote, he had already been on missionary journeys and established churches, so he wrote to admonish and encourage them.