There are 17 people specifically called an "apostle" in the bible, including the Lord Jesus Christ. But "The Twelve" is what we are talking about. The word "apostle" is a transliteration of αποστολος, one of two Greek words meaning "messenger" (the other is αγγελος from which we derive the word "angel").
There are messengers (αποστολος) who were not part of The Twelve, it is The Twelve who will have their names on the twelve foundations of the Heavenly Jerusalem.
Paul was not one of "The Twelve" as he did not meet the criteria Peter iterated in Acts 1.
Paul says he was a messenger, sent from God, with a specific message (the gospel) to a specific people (gentiles). He makes that very clear in Romans 1:1 "Paul, a servant of Jesus Christ, called to be a messenger, set apart for the Good News of God."
In fact he says the same thing over and over.
1 Corinthians 1:1 Paul, called to be a messenger of Jesus Christ through the will of God.
1 Corinthians15:9 For I am the least of the messengers, who is not worthy to be called a messenger, because I persecuted the assembly of God.
Galatians 1:1 Paul, a messenger (not from men, nor through man, but through Jesus Christ, and God the Father, who raised him from the dead),
Ephesians 1:1 Paul, a messenger of Christ Jesus through the will of God, to the saints who are at Ephesus, and the faithful in Christ Jesus:
Colossians 1:1 Paul, a messenger of Christ Jesus through the will of God, and Timothy our brother,
1 Timothy 2:7 to which I was appointed a preacher and a messenger (I am telling the truth in Christ, not lying), a teacher of the Gentiles in faith and truth.
2 Timothy 1:11 For this, I was appointed as a preacher, a messenger, and a teacher of the Gentiles.
No. The gifts of the Spirit were given by God according to His will, at the time of conversion. Those gifts lasted for the life of the person gifted. What Paul is saying in 1 Corinthians is that the gifts were no longer being given to new converts, but those who already had the gifts were to be allowed to use them (forbid not to speak in tongues). But as those senior saints aged and died those gifts died with them. I use John as an example because he is one with whom we are all familiar and we have a pretty good idea when he died.
The only confusion seems to be on your part. Nobody who had a gift lost the gift (the gifts and calling of God are without repentance - Romans 11:29). The gifts given to the older saints at the time of their conversion continued to operate even though no new converts were being given the gifts.