A few questions I had as a believing Mormon that were never answered:
1. Are we meant to understand the scenario played out in the endowment ceremony as actual, literal history? Adam and Eve were supposed to be real people, of course, but did PeterJames&John actually visit them and exchange signs and tokens, etc.? Or is the story supposed to be mostly symbolic?
It is going to be tough going having a serious discussion about your questions in the telestial, Sophocles (the Pillsbury Doughboy had me cracking up, though, I must admit), but here goes.
I agree with others who have suggested that the purpose of throwing PP&J (not be confused with PB&J) into the Garden of Eden has to do with disrupting the attendant and throwing him or her off kilter. This is sacred space and stuff we are talking about. Not only is it not necessarily going to make sense the first (or millionth) time, but it is going to be so contradictory to our understanding that it takes us out of our normal everyday life and puts us in a very different type of environment. It is my understanding (though I can cite you no examples) that this is a common motif in establishing sacred space in other religious traditions, as well. I heard it on a Mormon Stories podcast last year, dealing with sacred space in the temple, or something like that.
2. What's the deal with Satan? Are we to understand that he actually appeared to Adam and Eve as a man or a serpent? Why was he wearing an apron? (Can a serpent wear an apron?) What did he mean when he said that he was only doing that which had been done in other worlds?
Here I think the idea of the endowment being a portrayal of historical occurrences may be weighing you down. Satan may not have "actually" appeared to Adam and Eve as anything. But symbolically (which is where the deep magic lies), Satan appeared to them as a man and as a serpent.
The serpent symoblism is very important. We tend to see serpents as just plain yucky and to be avoided. Ancient civilizations, including the one that produced Genesis, saw the serpent as a symbol of wisdom. Here, it is significant that the symbol of wisdom is enticing Adam and Eve to eat the fruit of the tree of knowledge. There is a connection here we are supposed to get.
Additionally, the serpent was a symbol of resurrection and new life, primarily because of its regular practice of sloughing off its skin. A nice connection exists for Christians who get this part of the symbolism. The healing aspect was dealt with by Moses by putting the brass serpent up on the rod to heal the people who would look at it. One can easily Christianize the story by having Moses place the symbol of resurrection on a pole to heal the people who have faith to gaze upon it. The Book of Mormon does this.
3. Throughout my time as an active, believing Mormon, it was common to hear people refer to deep doctrine that could only be discussed in the Celestial Room of the temple. I suspect most of this was mere posturing—in fact I seem to remember someone on ZLMB who would always deflect criticism with the claim that he could easily demolish your argument, but it would involve sacred truths that could only be revealed in the temple—but there were also instances where this was sincerely discussed as a real thing. Yet in all my time as a temple attending Mormon I never witnessed any discussion of doctrine in the Celestial Room, or anywhere else in the temple for that matter. Has anyone actually had a discussion of doctrinal matters in the temple that they wouldn't have had elsewhere?
The only discussions I have had in the celestial room may deal with my personal views on possible meanings of grips, tokens and key words in the temple. I think that is the only thing that is not supposed to be discussed outside the temple. Everything else is fair game, as far as I am concerned.
All the Best!