how many civilians during ancient greek were christian?

The answer is very few to begin with, a substantial minority by AD 300 and a majority by AD 395.

Christianity grew slowly (not least because the followers of Paul managed to get the followers of Jesus declared heretics in the 2nd century AD) but steadily, usually through slaves and women (who were deliberately targetted by Pauline Christians). It is difficult to get exact figures, but by the reign of Nero (AD 54-68) they were noticeable enough in Rome to be blamed (wrongly) for starting the Great Fire of AD 66. In the reign of Marcus Aurelius (AD 161-180) they were numerous enough to be noticed and considered a nuisance, and by the reign of Decius (AD 249-251) they were interfering to such an extent that he felt it necessary to suppress them. Diocletian (AD 284-305) felt it necessary to repeat the process, as did his immediate successors except for Constantine, who took measures to gain the support of what was evidently by then a substantial minority of Roman citizens in his bid for sole rule over the Empire.

When Constantine became sole Emperor in AD 324, he soon made Christianity the official religion of the Empire (and the next year laid down the official creed to suppress some bitter disputes between Christian sects). From then until the Empire was divided in AD 395 at Theodosius' death, Christians increased in numbers and became the majority of citizens in the Empire: exactly when is hard to determine, but the reign of Valentinian (AD 364-375) is probably the best guess.

By the time the Western Empire fell in AD 476, the vast majority (90%+) of its citizens were Christian.

In the beginning only the poor and unlucky were Christians, they were attracted to the ideas of heaven, and a better afterlife, etc. Gradually though, Christianity started appealing to more people, and by 325 AD Christianity was the Roman Empire's official religion.

In ancient Rome, Christianity gradually became an important religion. In the Roman Empire, there had always been a lot of religions, and these were relatively tolerated, as long as they did not pose a threat to the emperor.

Christianity did (Christians do not worship Caesar, they worship God), and therefore up until 313 AD Christians were persecuted. In 325 AD, Christianity became the official religion of the Roman Empire.

Romans adapted to it, as their main goal was to keep the empire strong and united, and knew Christianity was too strong to persecute any longer.

Hope that helped a little!

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Christianity was not founded until after the birth of Jesus Christ, which traditionally occurred in 1 AD (but more likely was sometime around 7 AD). The Greek period ended, in my opinion, in 146 BC with the destruction of Corinth by L. Mummius. I think 133 BC might also be an acceptable date, as that is when the kingdom of Pergamum was willed to Rome. In any case, this was before Christianity existed. Of course there were still Greeks around, but the Greek civilization is generally regarded as having ended centuries before Christ was born.

None, Christianity was founded centuries after the ancient Greeks.