Paul is one of the twelve apostles. He took Judas' place by the appointment of God. Christians are lively stones in the house of the Lord.
No.
Matthias replaced Judas.
“Therefore, of these men who have accompanied us all the time that the Lord Jesus went in and out among us,beginning from the baptism of John to that day when He was taken up from us, one of these must become a witness with us of His resurrection.”And they proposed two: Joseph called Barsabas, who was surnamed Justus, and Matthias.And they prayed and said, “You, O Lord, who know the hearts of all, show which of these two You have chosento take part in this ministry and apostleship from which Judas by transgression fell, that he might go to his own place.”And they cast their lots, and the lot fell on
Matthias. And he
was numbered with the eleven apostles. - Acts 1:21-26
http://www.biblegateway.com/passage/?search=Acts1:21-26&version=NKJV
Paul had a completely separate ministry from the Twelve.
But I make known to you, brethren, that the gospel which was preached by me is not according to man.For I neither received it from man, nor was I taught it, but it came through the revelation of Jesus Christ.For you have heard of my former conduct in Judaism, how I persecuted the church of God beyond measure and tried to destroy it.And I advanced in Judaism beyond many of my contemporaries in my own nation, being more exceedingly zealous for the traditions of my fathers.But when it pleased God, who separated me from my mother’s womb and called me through His grace,to reveal His Son in me, that I might preach Him among the Gentiles, I did not immediately confer with flesh and blood,nor did I go up to Jerusalem to those who were apostles before me; but I went to Arabia, and returned again to Damascus.Then after three years I went up to Jerusalem to see Peter, and remained with him fifteen days.But I saw none of the other apostles except James, the Lord’s brother.(Now concerning the things which I write to you, indeed, before God, I do not lie.)Afterward I went into the regions of Syria and Cilicia.And I was unknown by face to the churches of Judea which were in Christ.But they were hearing only, “He who formerly persecuted us now preaches the faith which he once tried to destroy.”And they glorified God in me. - Galatians 1:11-24
http://www.biblegateway.com/passage/?search=Galatians1:11-24&version=NKJV
Then after fourteen years I went up again to Jerusalem with Barnabas, and also took Titus with me.And I went up by revelation, and communicated to them that gospel which I preach among the Gentiles, but privately to those who were of reputation, lest by any means I might run, or had run, in vain.Yet not even Titus who was with me, being a Greek, was compelled to be circumcised.And this occurred because of false brethren secretly brought in (who came in by stealth to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage),to whom we did not yield submission even for an hour, that the truth of the gospel might continue with you.But from those who seemed to be something—whatever they were, it makes no difference to me; God shows personal favoritism to no man—for those who seemed to be something added nothing to me.But on the contrary, when they saw that the gospel for the uncircumcised had been committed to me, as the gospel for the circumcised was to Peter(for He who worked effectively in Peter for the apostleship to the circumcised also worked effectively in me toward the Gentiles),and when James, Cephas, and John, who seemed to be pillars, perceived the grace that had been given to me, they gave me and Barnabas the right hand of fellowship, that we should go to the Gentiles and they to the circumcised.They desired only that we should remember the poor, the very thing which I also was eager to do. - Galatians 2:1-10
http://www.biblegateway.com/passage/?search=Galatians2:1-10&version=NKJV