A general topic on "what started it all..."

[Ryft]

... and you have satisfied my question as to why if something exists, then something must have existed for all time (correct).

If space and time are combined into a single manifold (q.v. Einstein), then "existed for all time" does not imply eternity but, rather, terminates at this same singularity.

If science doesn't know, then why aren't scientists more open-minded toward religion?

First, a significant percentage of scientists are religious. Second, an even larger percentage of scientists (obviously including the religious ones) are open-minded toward religion; one can be atheistic and open-minded toward religion, in contradistinction to those like Richard Dawkins. Third, religion does not have a monopoly on speculations about the universe's origins; there are non-religious speculations (e.g., ekpyrotic cosmological model).

Is it easier to not know? than to go down the path of learning to 'know'?

It all depends on how one proposes that we know anything. Those who advocate Scientism, whether explicitly or implicitly (e.g., leo-rcc), hold that even epistemology is subject to the authority of science, which means they would insist that "the path of learning to know" stops where science stops, at the singularity.

Is it easier to not know? Well, ignorance takes less work, yeah.

I often hear scientists suggest that religion and science are separate magisteria which do not interact. Yet scientists often start out Christians and convert to atheism during the course of their studies. So there truly must be some interactions between the two paradigms

First, it again all depends on the person's philosophy or worldview. Stephen Jay Gould proposed non-overlapping magisteria (NOMA), Richard Dawkins thinks Gould is talking nonsense for allowing religion any quarter (only one magisteria or OOMA), and Alister McGrath proposed partially overlapping magisteria (POMA). Second, there are also many scientists who start out as atheists and convert to Christianity during the course of their studies (e.g., John Polkinghorne). Third, conversion anecdotes have no substantive relevance beyond biographical information.