Do we have a divine mandate, command to heal the sick? Do only certain people get to be used who have these gifs of power? What is the conditions, spiritual criteria to operate in signs and wonders?

ONLY BELIEVE

Mark 16:17 And these signs will follow those who believe: In My name they will cast out demons; they will speak with new tongues; they will take up serpents; and if they drink anything deadly, it will by no means hurt them; they will lay hands on the sick, and they will recover.”

these signs will follow those WHO BELIEVE

SIGNS OF AN APOSTLE

Paul was not only an accurate theologian, dividing the Word, but he operated in the supernatural!!
Spirit & Word is the divine ingredients for new creations to take place

Acts 5:12 through the HANDS OF THE APOSTLES many signs and wonders were done among the people.
Acts 2:43 Then fear came upon every soul, and many wonders and signs were done through the apostles.
James 5:14 And the PRAYER OF FAITH will save the sick, and the Lord will raise him up.
He who believes: John 3:18, 36; Acts 2:38; 16:30, 31; Rom. 10:8–10
2 Corinthians 12:11-12 I have become a fool in boasting; you have compelled me. For I ought to have been commended by you; for in nothing was I behind the most eminent apostles, though I am nothing. Truly the signs of an apostle were accomplished among you with all perseverance, in SIGNS AND WONDERS AND MIGHTY DEEDS.
Acts 14:3 Therefore they stayed there a long time, speaking boldly in the Lord, who was bearing witness to the word of His grace, GRANTING SIGNS AND WONDERS to be done by their hands.
Rom. 15:18-21 in mighty signs and wonders, by the POWER OF THE SPIRIT of God
Acts 15:12 DECLARING how many miracles and wonders God had worked through them among the Gentiles.
Acts 19:11 Now God worked UNUSUAL MIRACLES by the hands of Paul, so that even handkerchiefs or aprons were brought from his body to the sick, and the diseases left them and the evil spirits went out of them.

GOD BEARING WITNESS CONFIRMING THEIR WORDS

God does not confirm the person, he confirms His word. The word of our testimony.
Declaring the gospel of salvation stirs faith for people to get saved, in the same way declaring god is present to heal, stirs faith for healing.

Mark 16:20 And they went out and preached everywhere, the Lord working with them and confirming the word through the accompanying signs.
Acts 4:29-30 grant to Your servants that with all boldness they may speak Your word, by stretching out Your hand to heal, and that signs and wonders may be done through the name of Your holy Servant Jesus.”
Heb. 2:4 God also bearing witness both with signs and wonders, with various miracles, and gifts of the Holy Spirit, according to His own will?

You cannot theorize the work of the supernatural. If you never have done it, you have no right to even an opinion.
The Kingdom is not in words only but power 1 Cor 4:20; 2:4 but in demonstration of the Spirit and of power, that your faith should not be in the wisdom of men but in the power of God.

If their is thus no signs and wonders, no miraculous, people put their faith in vain in the wisdom of man.

PEOPLE CAME TO THE FAITH AFTER THEY SAW THE DEMONSTRATION OF THE SPIRIT THROUGH VARIOUS SIGNS AND WONDERS.

Many churches are losing the young people, falling away because there is no miracles:
We will not hide them . . . ; we will tell to the coming generation the glorious deeds of the LORD, and his might, and the wonders that he has done. He established a decree in Jacob, and appointed a law in Israel, which he commanded our ancestors to teach to their children; that the next generation might know them, the children yet unborn, and rise up and tell them to their children, so that they should set their hope in God, and not forget the works of God . . . and that they should not be like their ancestors . . . whose spirit was not faithful to God. . . . They forgot what he had done, and the miracles that he had shown them. Psalm 78: 4–11 NRSV, emphasis added

The disciples believed in Jesus after He turned water into wine in John 2: 1–11: “This, the first of his miraculous signs, Jesus performed at Cana in Galilee. He thus revealed his glory, and his disciples put their faith in him” (verse 11 NIV1984, emphasis added).

People believed in Jesus after He healed a royal official’s son from a distance in John 4: 43–54: “Then the father realized that this was the exact time at which Jesus had said to him, ‘Your son will live.’ So he and all his household believed” (verse 53 NIV1984, emphasis added).

There is no record that the healing of the man at the Pool of Bethesda in John 5: 1–9 caused anyone to come to faith, but this healing is followed by a passage in which Jesus deals with people believing in Him in order to pass from death to life (see John 5: 10–47, especially verse 24).

Five thousand people believed in Jesus after He multiplied bread and fish to feed them in John 6: 1–14: “After the people saw the miraculous sign that Jesus did, they began to say ‘Surely this is the Prophet who is to come into the world’” (verse 14 NIV1984). The term Prophet here is a messianic title. During the interbiblical period between the Old Testament and New Testament eras, one of the views was that the Messiah would be a Prophet. Another view was that Messiah would be a King, and another was that He would be both Prophet and King.

A man born blind believed in Jesus after Jesus healed him in John 9: “Then the man said, ‘Lord, I believe,’ and he worshiped him” (verse 38 NIV1984, emphasis added).

People believed in Jesus after He raised Lazarus from the dead in John 11: “Therefore many of the Jews who had come to visit Mary, and had seen what Jesus did, put their faith in him” (verse 45 NIV1984, emphasis added).

Likewise, look what the chief priests and Pharisees were thinking after that miraculous sign: “‘ What are we accomplishing?’ they asked. ‘Here is this man performing many miraculous signs. If we let him go on like this, everyone will believe in him, and then the Romans will come and take away both our place and our nation’” (verses 47–48 NIV1984, emphasis added).

John 12 also records more fruit of belief from the raising of Lazarus: “Meanwhile a large crowd of Jews found out that Jesus was there and came, not only because of him but also to see Lazarus, whom he had raised from the dead. So the chief priests made plans to kill Lazarus as well, for on account of him many of the Jews were going over to Jesus and putting their faith in him” (verses 9–11 NIV1984, emphasis added).

Following the resurrection, the disciples put their faith in Jesus again in John 21: 1–7, after they miraculously caught so many fish by switching the net to the other side of the boat, as He had instructed them to do: “Then the disciple whom Jesus loved said to Peter, ‘It is the Lord!’” (verse 7 NIV1984).

Praat saam