The OP appears to ask about two things. One is biblical manuscript veracity and about historical sources regarding the existence of Christ. This answer is about the latter.
There are a number of sources that attest to Christ Jesus as an historical figure. The Old Testament, of course, prophesies of a Messiah, but who? In the New Testament, we know of Him as Jesus Christ. Are there non Scriptural sources that know of Jesus? We will look at four (Clement of Rome about 95 CE, Tacitus about 116 CE, Josephus about 95 CE, Pliny the Younger about 112 CE) who answer in the affirmative.
To be sure, these references are not without controversy, but they are satisfactorily addressed and clarified. Thus, there is no doubt that a man called Jesus Christ walked the earth and was witnessed about.
CLEMENT OF ROME
While Clement is a Christian, he is also a very early non-canonical witness to Christ Jesus.
The Church of God which sojourns at Rome, to the Church of God sojourning at Corinth, to them that are called and sanctified by the will of God, through our Lord Jesus Christ: Grace unto you, and peace, from Almighty God through Jesus Christ, be multiplied.
With Tertullian writing about 210 CE, we will back into the earlier witness of Tacitus who also wrote about Jesus Christ.
But having asserted that our religion is supported by the writings of the Jews, the oldest which exist, though it is generally known, and we fully admit that it dates from a comparatively recent period—no further back indeed than the reign of Tiberius—
Do we accept this account of Tiberias from Tacitus?
Reign of Tiberius 9/18/14-3/16/37 AD
The Senate convened on 18 September, to validate Tiberius's position as Princeps and, as it had done with Augustus before, extend the powers of the position to him. These proceedings are fully accounted by Tacitus.
As such, we also have Tacitus’ accounts of Christ.
Tacitus wrote the Annals about 116 CE. From this, we find the reference to Christians (or Chrestians) and Christ.
Consequently, to get rid of the report, Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judæa, the first source of the evil, but even in Rome, where all things hideous and shameful from every part of the world find their centre and become popular. Accordingly, an arrest was first made of all who pleaded guilty; then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind.
Josephus also wrote about 95 CE about Christ, His brother James, and Christians in Antiquities 20.9.1 and 18.3.3.
Festus was now dead, and Albinus was but upon the road; so he assembled the sanhedrim of judges, and brought before them the brother of Jesus, who was called Christ,
Now there was about this time Jesus, a wise man, if it be lawful to call him a man; for he was a doer of wonderful works, a teacher of such men as receive the truth with pleasure. He drew over to him both many of the Jews and many of the Gentiles. He was [the] Christ. And when Pilate, at the suggestion of the principal men amongst us, had condemned him to the cross,541 those that loved him at the first did not forsake him; for he appeared to them alive again the third day;542 as the divine prophets had foretold these and ten thousand other wonderful things concerning him. And the tribe of Christians, so named from him, are not extinct at this day.
PLINY THE YOUNGER
He writes to the Emperor Trajan about 112 CE regarding Christ and Christians.
They asserted, however, that the sum and substance of their fault or error had been that they were accustomed to meet on a fixed day before dawn and sing responsively a hymn to Christ as to a god, and to bind themselves by oath, not to some crime, but not to commit fraud, theft, or adultery, not falsify their trust, nor to refuse to return a trust when called upon to do so.
In sum, it is only the uninformed and misguided who do not believe there was a man called Jesus Christ who walked the earth and had followers after his death (and resurrection) that were called Christians. Historic references to Christ may be found from foe and friend. The real dispute is not whether Jesus Christ lived or even if He was crucified or had followers, but whether He rose from the dead.
For further references