Also if the bible was written by witnesses who walked with Jesus, why does it have so many different versions?
The "versions" that you speak of are merely TRANSLATIONS from the original language into english. The problem is that sometimes false teachers come in and try to twist up the scripture using translations which are not accurate. The bible was written in hebrew, greek and aramaic, NOT english. The KJV is the most widely accepted "accurate" translation of any other.
Do their stories not add up? Shouldn't the message be the same? Yet there are "versions" of the text?
They add up, see my response in bold above.
Jesus was sent to the house of Israel and to guide lost children of Israel, so how does his message apply to Romans who later adopted Christianity?
The Jews are God's chosen people because the "messiah" which means "Savior", Jesus Christ came through them. The gospel message went to them first, but because they rejected it, God allowed it to go out unto the gentiles (non-Jews) so that all men might be saved.
Isn't it true that Romans changed the bible's teaching and many of the celebrated holidays today have pagan roots and Jesus infact was NOT born on December 25th?
Yes it is true that the Catholics started the tradition of celebrating the birth of Christ on the pegan holiday of December 25. The reason was that many of the new converts had previously worshipped false gods. They decided to replace that false god tradition with the birth of Christ, since no one actually knows when Jesus was born. There is nothing wrong with celebrating the birth of Christ, but it's not mandated by the bible.
If all these are inaccuraries, then how can you be so sure they didn't flipflop the holy scripture as well?
Because we have the ancient manuscripts to compare to the bible.
Unless you have lived since those days and most certainly certify to the bible being genuine. :) Again...going back to "versions" of bible.
One doesn't have to live since those days to know that the manuscripts are still the complete word of God as originally penned by the eyewitnesses.
My responses are in bold.