Ok...

Pyramids are logical constructions, they are basically the only constructions besides mounds that could be made big. But unlike mounds pyramids can be made smaller atthe base, making them more impressive to the eye. Even the mesopotamian ziggurats were pyramidshaped if they had been continued to the end (gotten a point). So the shape ofthe pyramid is a most logical one.
One layer on top of another, slight smaller each time. A sound and solid construction with the least amount of problems.
Talk to a buildingengineer and he will tell you that.

I don't know here you have that religionstuff, but the religions are not similar. We have everything from ghostlike deities in Shinto, over bog-gods, tree spirits to pantheons of god, to monotheistic religions of many types (Zoroastriarism for instance is not like our version of Monotheistic religion).
But if we were to go back to the first religious people we would likely be able to recognize it as something we can relate to. Why? Because humans are remarkably similar in their beliefs and what scares them. We are afraid of the unknown, so we try to make it sensible so it isn't so scary anymore.

A serious flood happend twice (but many smaller ones have happend logically). First with the breaktrough at Gibraltar, then at Bosperus. The latter seems the originator of the biblical floodstory, a similar story is prevalent in many societies. Quite likely because many people lost their homes when the oceans rose in rushes (lakes spilling into the ocean and so on after the melting of the ice). That is why it is so common, though interestingly it lack from areas that were not affected by the rising seas, and it makes sense.
The nothern shore of the Black Sea is highly fertile, and thus it is a logical origin of many human tribes in the west. The now lost land must be assumed to have been equally fertile. Thus the Black Sea flood was a nasty shock, especially since the land lost was massive and very fast (flat country makes for a quick covering).
Imagine that you live 30km from the sea. You go to bed, and when you get up the next day you have water splashing around your feet. Outside it streches into the horison... That would be damn scary. You wouldn't know where to go...