Good to hear from you again. Let me assure you at the start that there is no cause for alarm at the existence of loose parallels to the Bible existing in other literature. The Bible is the truth. All other literature is man-made.
As I may have mentioned before, just what the Sumerian texts said is a matter of great debate in the scholarly community. It has been quipped that "there are as many Sumerian languages as there are Sumerologists", and that witticism tells us quite a lot. Much of what we know of Sumerian comes from Babylonian-Assyrian translations of their documents; the Sumerian language itself on its own terms has not been completely and adequately deciphered. This, and the issue of transmission of their texts through the Semitic, Babylonian-Assyrian language (Sumerian is generally considered an isolate; it is not Semitic), means that there is more than a little doubt about what was actually written, not something that is the case for the Bible.
To begin with the seven tablets, what we are dealing with here is the Enuma Elish, the Sumerian creation epic. However, our texts for this epic are not in Sumerian but in Babylonian-Assyrian, and they do not date to the days of the Sumerian civilization, but to the 7th cent. B.C., that is, 800 or so years after the writing of Genesis. There are some loose parallels (man created on the sixth day, for example), but it does not take much comparison to see that the two documents are more different than they are similar. It is a politically unpopular position, but I think it is actually much more likely that the Sumerian epic, whatever it originally looked like, was modified over the centuries and adapted to the Babylonian-Assyrian likes and dislikes, and that in that process of modification the biblical story was molded into it (i.e., the Bible influencing the final form of the Enuma Elish rather than the other way around). After all, it is not as though these civilizations were unaware of one another or of one another's literature. Even if we would wish to see this epic as pre-dating the Bible, that does not mean that it influenced Moses. It most certainly did not. He received the truth of what actually happened directly from God.
How, in such a case, would some semblance of truth have ended up in the Sumerian epic (again, assuming that it really does pre-date Genesis – something not at all clear since what survives does not)? Satanic influence should certainly not be overlooked. The demons know who God is – and they shudder. They were around when these events transpired, and the devil is the father of lies; he always delights in twisting the truth. Indeed, his best lies always have some semblance of truth contained within them and highlighted (as bait in order to get the innocent to accept the lie: see the link: in BB 3A "The Fall of Man"). If he and his minions led the writer of this epic to fabricate the seven Genesis days to some degree, it wouldn't exactly be the first lie the devil has sponsored.
There is second possibility as well (although it is not mutually exclusive of the first). What the Bible relates about the creation and the flood is true; these things happened precisely as the Bible says. We can be sure that Adam and Eve did not forget about the garden once expelled from it; we can be sure that Noah and his sons and daughters in law did not forget about the flood once it was over; and it is certain that all involved in the tower of Babel would remember it their whole life long thereafter. These are three of the most significant pieces of historical information that one generation could pass on to the next, and it is certain that they did so – not with accuracy, of course. The verbal transmission of these events would alter the story, especially once it was combined with paganism as in the case of Sumer. So what we may have here are two tracks: 1) the human one, wherein truth becomes more and more obscured over time, mixed with lies, legends and pagan conceits, but retains some loose connection with the original events; and 2) the divine one, wherein God through His Spirit caused Moses to understand the precise truth of what had happened, and then write it down accurately in an eternal, divinely inspired record.
In either case, as I say, the idea that the Bible borrowed from pagan literature is an incorrect one (to say the nicest thing I can say about it). Those who reject the existence of God, the power of God, and the wisdom of God search for such solutions (and are often enlisted by the devil in concocting them), and invest them with a patina of scholarly authority – but that does not make them right.
Why does God allow this to happen? For the same reason He placed the tree of the knowledge of good and evil in the garden and did not restrict the devil from tempting Eve: we are here in this world to demonstrate how we shall choose; we are here to exercise our free will in responding to God (or failing to do so). That would be impossible to do in a real and meaningful way if there were no opposition. In this world of darkness, the light shines out perspicuously for those who desire to see it – precisely because it stands out in the darkness. But for all who choose darkness over light, "even their light becomes darkness" and "how great is that darkness" (Matt.6:23)!
As to the question on the universe, I find the immensity of it thrilling and very humbling. Contemplating that there are over 100 billion stars in our galaxy and 100 billion galaxies or more in the universe ought to be enough to demolish the arrogance of the most prideful person and put him in dust begging for God's mercy. For not only does the immensity of the universe – created by the Lord in an instant of time and maintained by His powerful Word (Heb.1:3) – bring us to see how great He is but also how small and insignificant we are. Surely, this is a large part of its message. After all, God could have made the universe much bigger or much smaller; He made it exactly the right size in relation to our size and the size of the angels to teach us the lessons He wanted us to learn and to accomplish all His good purposes.
In my reading of Revelation, the New Heavens and New Earth (see the link) are likely to be much larger than today, and proportionately so in comparison to the greatly increased size of New Jerusalem. We will have all eternity to explore them, and in an eternity we will not be able to get to the bottom of them. But however great the universe is today, and however much greater it will be on that great day of eternity, it will always be insignificantly small in comparison to the One who made it. He made it for us, and we shall inhabit it forever with Him. Praise be to our Lord Jesus who died that we might experience all these things with Him forevermore!