Did Paul intentionally plan his letters so there would be seven Church Epistles?
No. Paul did not deliberately arrange his letters to produce seven Church Epistles. He simply wrote each letter as the occasion was appropriate, and it happened that seven were written for the Church. The number seven reflects God's perfect number, but it was not the result of Paul's planning.
Les explains that Paul's Church Epistles are seven letters written to the Church. He contrasts any human design with the way all the Bible fits together from Genesis to Revelation, saying no human could have dreamed it up. Les asks whether Paul agonized over dividing his letters to come up with the number seven, which is God's perfect number, and answers no. Paul wrote those letters as it was appropriate, and it simply fell out that there were seven written for the Church.