Hi, well I have had the same idea as you vis a vis adding bits on to any definition and finding that the new piece of the jigsaw was now included as an integral part of the newly considered "universe".
Describing the universe as everything that exists was not my idea. That's the way an ordinary English dictionary may define the universe. Here's an example:
Universe, (Noun)
everything that exists, especially all physical matter, including all the stars, planets, galaxies, etc. in space:
[Taken from the Cambridge dictionary, available online]
Most scientists do not claim to know everything that exists. If we try to discuss the remainder of your post using this sort of definition for the universe then we will rapidly run out of what is considered to be established science and plunge into conjecture. There is nothing wrong with a good abstract or philosophical discussion but I'm not sure that it can be done here in this forum.
What is the (entire) Universe and how does it work? I don't know... but we can define and try to build models for something called the observable universe.
There's a video from "MinutePhysics" that discusses the issue rapidly. [Not sure I can post links as a "Newbie" to this forum but you can find it yourself on YouTube with the title What is the Universe? - MinutePhysics]
prior to what is called the Big Bang.
This is another problem. It's not clear that there was any quantity or parameter that behaved like time BEFORE the big bang.
Would that observer,so defined have a bird's eye view of the process and would his/her/its(other) view actually be any different from the view it may be possible for us to achieve through mathematical/technological ingenuity, or even in our "mind's eye) ?
You have a good imagination and an interest, which is great. I am less able, I can't easily imagine an observer defined in the way you described. I'm certain that such an observer is not well defined within the context of mainstream science and so I'm confident that (current) Science won't provide many good answers to your question. I'm very sorry about this.
You continue to ask about borders...
I have come across (and possibly suffered from) the misconception that the (loosely defined) universe has a clearly defined border or edge border .
The Observable universe has a border or clearly defined edge but it is simply the limit (in terms of distance) that we have been able to see light from other parts of the Universe, so far. It is not a physical wall of any kind. If we could travel there in a spaceship, we wouldn't expect to find anything different about that region of space to any other. We do not know what is beyond the observable universe but we expect it to be much the same kind of thing that exists within the observable universe.
There are several Cosmological models of the universe that I have studied and none of them need to have any sort of physical border. Even if you consider a universe with closed (spherical) geometry that may have finite extent there still doesn't need to be any border (since we should only consider what can be observed intrinsically). I am not saying there isn't any model with such a border, just that there doesn't need to be one.
Best Wishes to you, sorry I couldn't be more help.