Welcome Singulatarian!
I am sorry that he JREF was it's usual self and got cranky before addressing your post.

to all,
b]The main issue is this:
When Hubble noticed the galaxies were moving away at a rate proportional to the distance that they appear to have from the earth. This observation is more and more fine tuned over time. So unless you find a way to red shift light that is proportional to its distance from the observer, the conclusion is that the universe is expanding.
This is the data and the hypothesis to explain the data. [1] [/b]
Then someone (many someones) decided to say "Hmmm, what is a consequence of this hypothesis?" And they said what would the consequence be of the expansion of the universe, and they created a model/theory where they theoretically ran the expansion of the universe in reverse. Hoyle did not like this and he dubbed it the Big Bang.
So far that is it, the theory does not state what started the BBE nor does it speculate as to the cause of the BBE, it just assumes the universe is expanding and then goes backwards. It is a very effective theory that matches the observations up to a point very shortly after the BBE.[2]
I am not a physicist.
First ground vs. excited state: this is not a question that the BBT can answer at this time.
Second: time. Um the model breaks down at ~10
-47-10
-36 after the BBE, one of many issues is quantum reconciliation with relativity. Partly the some issues are resolved with inflationary theory. But my understanding also breaks down at this point, where you have infinities at scales.
Third: inflation. It is a theory and there seems to be a clinging to older models, the universe does not care what our presuppositions are, it is what it is. Some may cling to older notions of what the universe has to be.
Fourth: Ex nihilio, the common philosophical objection of most BBE detractors, including Hoyle. The universe may or may not have come from nothing. We do not know and can not say at this time. That is the nothing of the BBE, what we can currently say about the universe prior to the BBE> It seems likely it came from something but that is speculative.
Fifth multiple space times: they are a consequence of some of the models of both quantum physics and inflation. They are however theoretical constructs and interpretive speculation in many cases. They are not required by the BBT because it just states: the universe appears to be expanding and then goes from there. the model does not state what is outside the universe or prior to the BBE.