The Bible Not Making Sense

Why did I leave Christianity and convert to Islam,? people often ask me, they often invite me to talk at meetings, on the issue.
Its not difficult  to explain as it is not for others, also that  left to become Muslim and I'm seeing literally hundreds including vicars and Bishops, catholics all converting.
Small things not big issues but its really just common sense, that if the small things don't add up, how on earth are the big things going to.
I did not understand who Mark, Luke, Mathew and John were? meaning the gospels according too? The word according, according to who? as we don't even know their surnames, their backgrounds.
What bible do we look at?  When I was training to become a Baptist preacher I  was told in my studies to use a number of bibles , but then I'm told the bible is the word of God. My issue  then became, what about theit  footnotes at the bottom of some bibles? if this is the word of God why footnotes?

Another point that I could not deal with, is the trinity. This is what  brings so many into Islam due to the trinity.
When I studied the Old testament it refers to one God, suddenly in the so called new testament there are three.
Then some Christians give a different story that Jesus was the son of God, others say he was God,  others say he was a holy ghost, so what is the correct answer?
The birth of Jesus is celebrated with the celebration of Christmas, but when I was studying to become a minister I could not find the word in any bible?
In my studies as well as others, we could not even come across December the 25th, so where did that come from? Why are Christians celebrating this day when Jesus  was not born on this day?
Regarding the cross, in the days of Jesus they did not crucify people on the cross, but on tee shape poles and  uprights.
One big issue is even today globally the Christmas tree is decorated in the households, but in the bible it is forbidden, so is interest, alcohol and pork.
If Jesus was God, then why did he say what he said on the cross? If your not sure look it up and see for yourself and he spoke his language which was?, but Christians seem to not know this.
Then  I find Jesus and  other prophets fasted, like Muslims, they even washed for prayer like Muslim, they prayed like we do.
I have not included a whole list of verses, pages as it would take a whole book to explain, but all I'm doing is pointing out some and not all of the reasons why I left that religion and became Muslim.
If you get chance  look for yourself and do your own research and see what you come up with.