I want to point out a few things to reflect on. Stephen would have been one of those who received the Holy Spirit at Pentecost, as he would have been one of the disciples who were present with the Apostles and the Virgin Mary.
The Apostles gave him the "assignment" of collecting food for the poor. It is while doing that charity that he came into conflict with "The Synagogue of Freedmen, Cyrenians, and Alexanderians, and also people from Cilicia and Asia," (Acts 6, 9) who challenged him. It was not the collection of food that concerned them, but they envied the spirituality of St. Stephen because since the Pentecost he was a miracle worker (Acts 6:8). This is an example of one of the grave sins against the Holy Spirit, which is to envy someone else's spirituality and goodness.
I also can't help but point out that it sounds like a "gang" that assembled directly after the crucifixion and resurrection of Jesus to refute him and his Apostles and disciples. For history buffs, if something "did not happen" then why did such a motley gang, such is spelled out in such detail in the above passage, wander the streets to hunt down charity and miracle workers, hmm? Yet so soon after the death and resurrection of Jesus there just happened to appear such an interesting array of people, led by members of one synagogue, to hunt down his followers. "Things that make you go, hmm." In fact if you study Acts you will read how for years people gathered in "gangs" to hunt down Apostles and the people that they ministered. So the first days of Christianity was not, despite what today's so called intellectual "talking heads" try to say, "just another Jewish cult." Jewish cults were tolerated by other Jews; they certainly were not hunted down by gangs of people from as far away as Asia, recruited by synagogue members. Where there is smoke there is fire. And two plus two equals four. The evidence is there for anyone who reads and comprehends the witnessing of events recorded in the New Testament.
I also want to point out that it was the Holy Spirit who enabled the Apostles and some disciples to perform miracles in the name of Jesus. The receipt of the Holy Spirit at Pentecost is not the same as people who think they "have" the holy spirit today. This was a one time sending of pure grace and charisms by God through the intercession of Jesus Christ. This was why Peter and the other Apostles and disciples were able to perform miracles. Remember that Mary received this too, although her activities are not recorded because she was "family" not a worker of the early Church.
I also want to point out that it was this Holy Spirit that allowed the heavens to actually open up and St. Stephen to see heaven as he was about to be martyred:
But he, filled with the Holy Spirit, looked up intently to heaven and saw the glory of God and Jesus standing at the right hand of God, and he said, 'Behold, I see the heavens opened and the Son of Man standing at the right hand of God' (Acts 8: 56-57).
In fact it was seeing heaven that infuriated his persecutors even more and it was at that time they dragged him out of the city and stoned him. Again, this is why envy of someone else's holiness is such a grave sin against the Holy Spirit.
Remember though that with God all is never totally lost. Saul stood by and watched the persecutors cloaks for them while they stoned St. Stephen. Saul would fall on the Road to Damascus when the resurrected Jesus Christ confronted him, and thus Saul became St. Paul.
St. Paul received "Pentecost" directly from Jesus, by the way, which is the reason that St. Paul could work miracles of the level of the Apostles themselves.
St. Stephen was also the first martyr to pray for and forgive his persecutors as they killed him. This is not a requirement, by the way, but shows the exemplary grace that he contained within him.
