On No. 1, @Elle provided you a link to an article that discussed the symbolism of numbers in Genesis. Did you even look at it? Here are a few excerpts that answer most of your questions:
"There are 30 age numbers we can get from Genesis chapter 5—three numbers for each of ten patriarchs: the age when a son was born, the number of years the patriarch lived after the son was born, and the total number of years the patriarch lived. … The first thing more careful observation reveals about these 30 numbers is that all of them end with the digits 0, 2, 5, 7, or 9. You might not think that is too remarkable until you realize that it eliminates half of the possible numbers. It is like seeing a list of 30 numbers that are all even. We wouldn’t think that was a random distribution of numbers. In fact, the odds of getting all thirty numbers to end with just these “approved” digits in a random distribution of ages are about one in a hundred million. That should make us suspicious that Genesis 5 is merely giving a historical report. Something else must be going on here.
"One option is attaching some significance to the fact that all of the 30 numbers can be expressed as combinations of the two “sacred” numbers 60 and 7 in terms of years and months. 60 was culturally significant because it was the number that Babylonian mathematics was based on (the influence of this sexagesimal system is still felt today with our 60 minutes per hour and 60 seconds per minute). And 7, of course, has a prominent place in biblical symbolism beginning with the Sabbath. So when we’re told that Methuselah was 187 years when he had his son Lamech (Gen. 5:25), we can see that 187 = 60+60+60+7 years. And then because 60 months = 5 years, when Adam is said to be 130 years at the birth of his son Seth (Gen. 5:3), that can be expressed as (60+60 years) + (60+60 months).
"This could explain why all the reported ages end in 0, 2, 5, 7, or 9. These are what common combinations of 60 years, 5 years (=60 months), and 7 years end with: besides the obvious 0, 5, and 7, numbers ending with 2 come from adding 7 to a number that ends with 5; and 9 comes from adding 7 twice to a number ending with 5.
“For some of the numbers in Genesis 5, the combinations have to get more complicated. Check the footnotes to see how to calculate Seth’s 912 years when he died, or the 782 years Methuselah lived after the birth of Lamech. These and all the others can be generated by combinations of 60, 5, and 7.”
If you ask a question and someone provides a resource, perhaps you should check it out.
Say what? Where in the Scripture is the symbolism behind the number 7 explained? Chapter and verse, please. The symbolism behind numbers was a feature of the culture, just as superstitions about the number 13 are a feature of various cultures (including ours). If you are reading and run across the number 13 prominently used, you don’t need someone to explain its meaning to you, and the author doesn’t feel compelled to explain what everyone already knows, either. The same concept applied to the numbers used symbolically in Scripture. The author didn’t have to explain to the ancient audience the meaning of the numbers, because he assumed they already knew the meaning. Unfortunately, over the course of thousands of years, the symbolic meanings were gradually forgotten. It is the job of scholars to research the past and try to recover these forgotten meanings.
You keep coming around to this argument. Why? It’s like saying, “But God wouldn’t do it that way!” Here’s a good comparison – the textual history of the New Testament. Over the course of many centuries, scribes and copyists made errors and additions that gradually made their way into the text. During the last several hundred years, numerous manuscript discoveries and the hard work of many scholars have allowed us to substantially “recover” the most likely original readings of the Greek New Testament.
Now, why would God do it this way? Why would he allow generations of Christians to read the longer ending of Mark (16:9-20) or the woman caught in adultery (John 7:53-8:11) and think it was part of his holy word? Many of the “King James only” crowd used this line of argument, but I somehow doubt it keeps you from reading modern translations.
In short, why wouldn’t God do it that way? Why would he hand everything to us on a silver platter? Does he work that way in your life? Does he grant you knowledge with no effort, no study? As Augustine said, “In every page of these Scriptures, while I pursue my search as a son of Adam in the sweat of my brow, Christ either openly or covertly meets and refreshes me. Where the discovery is laborious my ardor is increased, and the spoil obtained is eagerly devoured, and is hidden in my heart for my nourishment.”
Who said Genesis wasn’t meant to be viewed as history? Gen. 1-11 is history, but it is not historical narrative. There are clues all throughout that section that we are not dealing with a straightforward retelling of history. What it is, in my view, is a prophetic critique of the progress of human culture and sinfulness. Just as Isaiah can use symbols to describe the distant future, “Moses” can use symbols to describe the distant past. In that sense, the symbols are “historical” in that they tell us something truthful and factual about the distant future or past, but they are not historical in the sense that the events literally took place, or that men actually lived to be many hundreds of years old. That is not how symbolism and metaphor work.
I’ll skip No. 4, since I believe “the man” is an archetypal symbol.
On “gaps” in the genealogies, the classic treatment is by William Green in 1890. In “Primeval Chronology”, he shows by comparing Scripture to Scripture that the genealogies cannot be used to construct a chronology (6,000 years).
Edit: Click the link if you really want to learn and are not here just to debate.