To summarize your believes, there are multiple variants of the Bible with some passages having more authority then others. Some passages from these variants are more inspired by God and others are less inspired by God, but even the passages that are not inspired by God are true, even if the origins are not clear. If the words that were put into the mouth of Jesus in Mark16:15 never happened, it does not matter; this fact is common knowledge and only ignorant people are not aware that Jesus did not say these words. It sounds good even if not true. Anyone who does not know this common fact (as well as many others I am assuming) is not serious about studying the Bible.
Is this how you believe that the Almighty has chosen to communicate with all of mankind? God's officially-stamped version of communication with man by the Christian Church is through this myriad of textual variants and nuances in word meanings and languages that were spoken (oops, no...those particular words might not have been spoken unless you know the details dummy!). God purposefully buried all of this eternity-determining information for going either to heaven or hell in such a morass? It would take a lifetime to decipher what is the true inspired word of God, what is the almost true inspired word of God, and what is not. No one is going to make it up there if God purposefully did this.
Will you tell me that this paraphrased passage also has doubtful origins? The entire Bible can be summed up by these words whether you say that are inspired or they were written by the Biblical 1,000 monkeys.
Love God, and love your neighbor
Knowing the rest of the Bible is secondary to this and merely window dressing, IMO. Why devote so much time to deciphering the nuances in Bible passages when these verses are all that you need to know? Taking a walk in the forest would make many feel closer to God than spending years trying to figure-out who said what to whom thousands of years ago. I choose not to ascribe any violent acts to God. If you do, that is your choice. I hope that we can at least agree on this core passage from the Bible.