Was Peter known as a leader among the disciples at the time of Acts?

Yes as he was appointed as the leader of the Church Jesus established before dying to make it possible for humans to be free from the eternal consequences of sin.

http://www.sancta.org/rosary/how.html

The fifteen promises of Mary to Christians who recite the rosary:

1. Whoever shall faithfully serve me by the recitation of the Rosary shall receive signal graces.

2. I promise my special protection and the greatest graces to all those who shall recite the Rosary.

3. The Rosary shall be a powerful armor against Hell, it will destroy vice, decrease sin, and defeat heresies.

4. It will cause virtue and good works to flourish; it will obtain for souls the abundant mercy of God; it will withdraw the hearts of men from the love of the world and its vanities and will lead them to the desire of eternal things. Oh, that souls would sanctify themselves by this means.

5. The soul which recommends itself to me by the recitation of the Rosary, shall not perish.

6. Whoever shall recite the Rosary devoutly, applying himself to the consideration of its sacred mysteries, shall never be conquered by misfortune. God will not chastise him in His justice, he shall not perish by an unprovided death; if he be just, he shall remain in the grace of God and become worthy of eternal life.

7. Whoever shall have a true devotion for the Rosary shall not die without the Sacraments of the Church.

8. Those who are faithful to recite the Rosary shall have during their life and at their death the light of God and the plenitude of His graces; at the moment of death, they shall participate in the merits of the saints in Paradise.

9. I shall deliver from Purgatory those who have been devoted to the Rosary.

10. The faithful children of the Rosary shall merit a high degree of glory in Heaven.

11. You shall obtain all you ask of me by the recitation of the Rosary.

12. All those who propagate the Holy Rosary shall be aided by me in their necessities.

13. I have obtained from my Divine Son that all the advocates of the Rosary shall have for intercessors the entire Celestial Court during their life and at the hour of death.

14. All who recite the Rosary are my sons, and brothers of my only Son, Jesus Christ.

15. Devotion to my Rosary is a great sign of predestination.

Peter had preeminence in the Gospels, but he wasn't anything particularly special. In the book of Acts, James was the leader of the Jerusalem Church. And if any apostle can be said to be above the rest, that prestigious position would have to belong to St Paul, the only apostle Christ spoke to repeatedly post-ascension and the apostle who was single-handedly responsible for 75% of the New Testament and the Gospel message being spread throughout the Roman world.

Jesus taught that no men should be placed higher than any other but that whoever wanted to be greatest, had to be least.

The first disciples were considered "elder" because they had been with Jesus longer and had a better understanding of his teaching. Christianity began in Jerusalem. Only a handful of faithful ones like Paul, Mark, etc. made long journeys to spread the word. The churches they established in other places, looked to Jerusalem and the "elders" for encouragement and inspiration as well as the arbiter of disputes and problems.

For example, after Paul left one congregation, some within it began to persuade others that all new members, whether Jew or Gentile had to be circumcised. They did not understand fully that the old covenant laws had been replaced with the sacrifice of Jesus.

Many Jews still don't understand this

So they sent back to Jerusalem and the "elders" to settle the dispute. After careful deliberation and heartfelt prayer, the body of elders wrote back telling them that circumcision was no longer necessary.

Peter was only one of these men and not the leader of the church. There was no single leader. The men who directed the business of the early church had been baptized with holy spirit at Pentecost, remember? Along with 3000 others.

The group in Jerusalem were looked to for guidance because they had been with Jesus longer and were more "mature" in the truth.

The bible explains that after the death of the last apostle, apostasy entered the church and spread throughout it, corrupting it. It was not to be until; the "last days" that the true church would be reestablished.

It has been.We are living in the last days and God's congregation has been rebuilt by those seeking the truth. It is constructed and operated just as the original church was, as Jesus taught. It is governed by a body of older, more "mature" men who are guided by Jesus who is their leader, by God's appointment.

They have laid down their weapons, as He instructed and are fulfilling the prophecy at Matthew 24:14, to preach the truth throughout the world as a warning and an invitation for all men to repent as the end is very near.

Please see Micah chapter 4.

Jesus taught that we are not to look to any man as our leader but to him as the king of the kingdom of heaven. This is God's arrangement.

The main characters of Acts are Peter and Paul.

It's simple look how St. Luke wrote about the Apostles he addressed them as "Peter and the Apostles". And within the Gospels when they listed the Apostles Peter (Simon) is always listed as the first of them. And again Jesus stated that upon St. Peter He would build His Church, and again three times Jesus entrusted St. Peter with His disciples. And no surprise after the Council of Jerusalem St. Peter exercised his authority as the leader and here St. James the Elder and St. John the Evangelist instructing the converts to observe the kosher dietary laws which St. Paul got upset at St. Peter. Even St. Paul had to report to St. Peter but St. Paul in his Epistle never called him Peter but Cephas in Greek.

St. Peter after leaving Jerusalem established the church of Antioch it was also said he had traveled to various places throughout Asia Minor before heading to Rome where he was martyred. St. Paul was in Rome and established the church there before St. Peter and the church of Rome after St. Paul was martyred had no Bishop of Rome so St. Peter traveled there to reestablished the church of Rome. This is why today the church of Rome has two Patriarchs St. Peter and St. Paul. Now St. Mark the Evangelist was Ordained Bishop of Alexandria by St. Peter. St. Mark the Evangelist was a disciple of St. Peter in which when he wrote his Gospel was based upon the testimony of St. Peter so one could actually claim that the Gospel of St. Mark the Evangelist is the Gospel of St. Peter. And the successor of St. Peter is St. Linus of course for a while they would refer to the successors of the church of Rome as St. Peter and St. Paul like what St. Ignatius of Antioch wrote in his letter to the Bishop of Rome.

without a doubt. Jesus planted the church in jerusalem and peter was its first pastor. a monumental undertaking considering the incumbent religious regime.