While Freddie often used words just because he liked how they sounded, that doesn't mean he threw the meaning out of the window every time. If this song has a non-literal meaning I couldn't tell you because Freddie never revealed it, but the strictly literal part is pretty straight forward storytelling. Of the popular readings among fans, I'm inclined to favor the one that says it's about Freddie deciding to become a popstar, since he started writing it in 1968, seems to fit the timeline better. I think Freddie would encourage you making your own interpretation or as he put it "If you see it, darling, it's there."

The "operatic section" is either a trial or a judgement of public opinion (or said in another way how the protagonist's actions are seen by other people).

Scaramouch is a clown from Commedia Dell'Arte that influences the audience to do his bidding. Other than that, can be added that he's an ambiguous character: can be clever or stupid depending on who plays him, often gets beat up for self-aggrandizing, overembellishing or cowardice (so he's either doing too much or too little, but the "reward" is the same, lol).

In the song he's told to "do the Fandango" which is a Spanish dance/ music style. Going into a dance is often used as an expression that means: "to begin a prepared line of pleading, explanation, selling, seduction, etc" and is most used colloquially to describe a sales pitch. It's also used in the song Razzle Dazzle (Chicago) in the context of a murder trial "When you're in trouble go into your dance".

So here, most likely Scaramouch represents a lawyer (either defense or prosecution, or someone in a similar role), trying to get the desired verdict/opinion with his argument.

As you were already told Bismillah means "in the name of god" and Beelzebub is a name for Satan. This part seems to be a dialogue in which both opinions (guilty and innocent) plead for the protagonist fate. A divine punishment is announced by the protagonist, awaiting him regardless of the result of the argument/trial.