I was just reviewing a past question/answer on here. Is it true Mohammed did not really pen the Quran?

I read that it was written on leather, palm leaves and others but not preserved. I also read the Quran didnt actually show up until 150 years after Mohammed died. I also read that the Quran is just a copy of the Old and New Testaments with some pagen practices thrown in. And that if Allah was the one true God why did Abraham not call Him by His name? And my final question I read that the crescent moon was actually the family crest of Mohammed and Allah was a moon God. I guess it would be great for anyone to answer but perhaps Muslims could answer these questions best. I have done some research and found these same answers. The only one I found to be different is that Muslims say that the Jews changed what Abraham really called God name wise. Im not trying to discredit Islam just trying to get a better look at it. Thank you all in advance.