You fail to realize that the Dead Sea scrolls exist. Many studies have been done of current versions of Bibles. Good translations of the Bible, just like any other product in a free market, tend to rise to the top. Bible's such as the King James, New King James, North American Standard, etc have been vetted against the Dead Sea scrolls and found to be accurate. I will cede the fact that some minor words are different in those different versions of the Bible. However, the intent and purpose is not changed.
I am aware you don't believe in the Bible and I believe that is the crux of this entire debate.
God is God. He was, is, and will always be. So yes, it's the same God. God Himself did kill a lot of people in the OT. However, look at some examples of who He killed. Take Jericho, for instance. Those people burnt their sons and daughters as sacrifices to their gods. God took their city and gave it to a righteous people, the Israelites. Sodom and Gomorrah is another example. God allowed Abraham to "talk Him down" to the agreement that if he could find 10 righteous people in those cities, that God would spare them. The only people that made it out were Lot and his children.
You answered your own question about why he killed the human race. Which He did not kill all of btw. Honestly, the only answer I can think of with my human mind about the second one is that if the King had been "walking" with God to begin with, the incident may not have happened. However, that is theory and I can't answer that. I won't act like I have the answer to everything. I have faith that my God is just and righteous and He did it for a justified reason.
According to Bible, this is incorrect. See the other post to Boo Radley about it.
To me, it is a book of facts. As I said above, no other book has been vetted like the Bible has.
He killed people. He is our Judge. Why is that hard to understand? Does your God allow everyone into his heaven? If so, you will be meeting Hitler and Stalin when you go. God has to judge. It's part of the job for lack of better words.
Actually, judging you would be me saying that you are an idiot for believing what you believe. I am not doing that. I am merely stating my beliefs versus yours about the Bible.