There's still religions before Judaism though.
Oldest found isnt the oldest. The Hebrews were an oral culture even after the deluge. Let's forget about the antediluvian world, for now; assume those civilizations, but not the texts or history necessarily, were razed.
Sumer, Babylon, Phoenecia, (AS)Syria, Persia, Ancient Greece, Ancient Rome, Greece, Rome... all experienced the same phenomenon that influenced their culture, mythos and "religion and spiritual alignment." Texts from the antediluvian world tall about the same thing the bible talks about.
That doesn't mean the Hebrews stole the mythos.
In fact, the Apocrypha, which is basically banned in the West, is very much so descriptive about the events that happens during, before, after - any temporal location existent and to come. It is full of the same prophecies that are in the bible, but some of the books are from the antediluvian world - from Enoch, and Noah. Other books have been the controversial compliments of archaic texts, scrolls, petroglyphs and tablets pointing to the same unique stream of events described in the bible. Everyone's "religion" is a romanticism of the events that happened that affected the whole world - sans actual worship of the Most High. The gods and entities that tried to gain power "never letting a catastrophe go to waste, " were the ones who stole the truth and morphed it into a bunch of religiosity. But, the story is the same all over the world - look extremely close, and analyze the patterns.
When people say "bible," they mean the 66-book canon. There are many texts, philosophies, mythos, literature and general art that imitates life. Everyone is saying the same thing, with different romantically aligned motifs.
I over simplified it as I do know beliefs about hell vary considerably. If you go by the OT hell doesn't really exist. You just die. And You either get resurrected or you don't. But I think the mainstream is still that hell is eternal punishment.
Yep. As said, hell is romanticized via Gehenna. As you said, you die once and resurrect, never dying again, or you go to judgment and possibly did a second time.
It is eternal because you will never be able to resurrect as long as eternity exist. Clearly is it possible for you to resurrect if we believe Christianity. So, that is why the second death is eternal: you will NEVER be able to resurrect. No loopholes, no more sacrifices. Your essence is forever gone without chance of coming back.
The fire and brimstone is mostly pomp and circumstance.