As to looking for a "first" or primitive form of life millions or billions of years ago I am always going to think that is the wrong approach from an Epicurean perspective. I think Epicurus would insist that there is life throughout the universe, and that the universe had no beginning date. So whatever he would point to as producing this mechanism, or to be it's key characteristics, I do not think he would think that to be time-dependent. I think the appropriate analogy would be that no matter how many monkeys and how many typewriters and how many years those monkeys would never produce the works of Shakespeare. I am thinking it's likely the discussion would be more on the lines of something swerve-like in the sense of "it must be there and be natural even though we don't yet understand the mechanism."
Of course I am very open to alternate possibilities including being completely wrong on my view there.
But I think any theory that posits a "first" is going to be incompatible, as would any theory that violates what we can glean from the views of "isonomia" and "nature never produces only a single thing of a kind."
That's why I think If we want to talk "soups" that is one thing, but simply assigning something to millions of years ago is not helpful. Where we are today is going to be "millions of years ago" when a couple more millions of years pass by.