You're being slightly incoherent, slow down a bit.
I know the answer to the last one: they typically get screwed over mentally or otherwise like Odin did in the previous world. It's not race specific so much as it is "what I am/represent is not relevant or present in the minds of my new worshipers, so how do I exist?"
The Dark One being unique has nothing to do with the goblins themselves biologically speaking, just that [special stuff] happened that isn't normal. It could be disdain towards the preexisting pantheons or something entirely unique to the scenario itself (maybe something like that happens every few hundred worlds, but normally geography determines the quiddity in the ultra-specific scenario a god is raised without an influence from the pantheons but this time its different for some reason). TDO didn't raise himself, he ascended after his death due to the sheer amount of goblins devoting themselves to his cause and doing things in his name. The high birth rate of the goblins is a contributor to how TDO got powerful so quickly, you're right about that.
The Elven Gods were raised in this world. There were presumably some others raised before, and could have survived many worlds, but eventually died at a point prior to this one.