All of this (other than the inspiration of the Holy Spirit) is consistent with the same literary forms used by other cultures in the Ancient Near East. We attribute these stories to the inspiration of the Holy Spirit but that doesn't change their genre and method of narration. It doesn't change them into reportage like that of a journalist or historian.
No, it is cosmic in that it presents a destruction of "every living thing" on the face of the earth (or land). "He blotted out every living thing that was on the face of the ground, human beings and animals and creeping things and birds of the air; they were blotted out from the earth. Only Noah was left of those with him on the ark." Gen. 7:21 And later it traces all human peoples to Noah and his sons. There would be no point to those genealogies if the people formerly inhabiting those lands had not been completely destroyed and left no descendants.
In what sense? What do we have that tells us the intention of the story? Our best indication is Gen. 6:5 but that is part of the story too, so only provides the set up for the rest of the story.
Yes it does suggest the existence of civilizations. Right back in the story of Adam and Eve, you have reference to agriculture. Gen. 4:17 tells us that Cain founded a city and named it for his first son, Enoch. vs. 20-22 tells us of the three sons of Lamech who founded arts associated with civilization, including the use of bronze and iron. The flood story itself speaks of domesticated animals.
Local floods, yes. Leonard Wooley found a flood plain interrupting Sumerian civilization around that time with ruins of cities both above and below it. But there is no indication that flood touched Palestine or Syria or Egypt. There are other floods that did, of course, but they did not destroy Sumer. So there is no complete disruption of civilization even in the areas known to the biblical writers, much less globally.
Such a local flood could have been the historical root of a story such as we find in the Gilgamesh epic and its parallels, including scripture. But while that would root these stories in a historical event, the stories as told are not an accurate record of the events. They are stories inspired by the event not records of the event. Indeed, the story need not refer to any particular event at all.