Asking why something happens cannot operate in the infinitely determined or infinitely undetermined. — Paine

This sentence is a performative contradiction. You use explanation to make a declaration about the prohibition of explanation.

Whether it's an infinite regress of causes, postulated first causes, or a realm of pure chance, the way to the answer to why-being is endless.

Thinking and the object of thought are the same. For you will not find thought apart from being, nor either of them apart from utterance. Indeed, there is not any at all apart from being, because Fate has bound it together so as to be whole and unmovable. Accordingly, all the usual notions that mortals accept and rely on as if true---coming-to-be and perishing, being and not-being, change of place and variegated shades of color---these are nothing more than names. — Parmenides, 8: 34-41, Wheelwright Edition

Assuming thought only accessible through language of some type, I ask, "Was Parmenides a nominalist?"

“Why not nothing?” elicits the reasoning that reveals that math, logic, and science are incomplete and also that the universe is open (it didn’t start from nothing) and cannot be closed. — ucarr

Gödel proved that any mathematical system is necessarily incomplete, but this does not imply the "universe is open". Given the fact that there is a universe, it follows that there is not, and never was, a 'state of nothingness", that preceded it (temporally or causally). The reasoning is parallel to your support of your premise 1.

I suspect you wish to assume there did exist a prior state of "God sans universe". That's logically possible, but it's an unwarranted assumption. Here's why:

Define ToE: The Totality of Existence. If naturalism is true then ToE={the universe}; if deism is true then ToE={universe+God}

In either case (ToE) was not preceded by a "state of nothingness", for the reason I just mentioned: it is logically impossible for a "state of nothingness" to precede that which exists.

So, feel free to assume a God exists - but don't fool yourself into believing you can prove it to be the case.

I did not mean to express a prohibition. The Goddess implores the visitor to not try to say what is not sayable. She also observes that many do. The emphasis I put on conditions is to note that making 'what is not being' an object of thought is to ignore that we can only compare alternatives between beings. Hypothesizing the existence of a 'non-being' would be a division of being. It is this division that Parmenides objects to.

Assuming thought only accessible through language of some type, I ask, "Was Parmenides a nominalist?" — ucarr

Not in the sense the word is used today. The Goddess does not permit utterance to be separated from thinking. The whole issue of whether universals have an existence beyond a grouping of particulars, as nominalists deny, requires division Parmenides says are strictly the business of mortality.

Carl Sagan speculated about our universe being eternal. When does eternity begin? — ucarr

This has nothing to do with what I've said.

I don't know what "insuperable immersion in being" means. But as I said, I think the only meaningful question is "why does the universe exist?" No purported inquiry into "nothing" is needed to address that question.

Is there a logical escape from the somethingness that is the phenomenon of creating somethingness from nothingness? — ucarr

If so-called 'Nothing' has a capability to make something, then one didn't really have the claimed 'Nothing' in the first place, for capability is a something.

— Parmenides, 8: 34-41, Wheelwright Edition — Paine

My vid: https://www.youtube.com/watch?v=ydjBxed0Pm0

I fail to see your point.