I wrote a bit about Amadeus in a previous answer, which mostly focuses on his financial issues but touches on the central myth of the movie, that Salieri and Mozart were at odds. In fact, while there was a bit of a rivalry, they seemed to get along, and Salieri ended up teaching music to Mozart's son. Salieri did not poison him. But your answer about his personality actually gets to something that I think is very important about film portrayals in general, namely that it depends on what you mean by "accurate."

Film and stage portrayals are often stylized and/or exaggerated in order to make a particular point. For example, the recent movie The Blind Side told the mostly-true story of a kid in very poor circumstances who was taken in by a well-off family, and grew up to be an NFL player. The film shows him as struggling academically, and eventually finding his place on the football field after being coached up by his new family and high school coach.

The real-life guy, Michael Oher, later said

I felt like it portrayed me as dumb instead of as a kid who had never had consistent academic instruction and ended up thriving once he got it. Quinton Aaron did a great job acting the part, but I could not figure out why the director chose to show me as someone who had to be taught the game of football. Whether it was S.J. moving around ketchup bottles or Leigh Anne explaining to me what blocking is about, I watched those scenes thinking, 'No, that's not me at all! I've been studying — really studying — the game since I was a kid!' That was my main hang-up with the film.

The narrative of the film was to show this kid being brought from a real low point to a high point. In order to make it more dramatic, they made the movie Oher start at a lower point than the real-life Oher. Is it inaccurate? Factually, yes. But it drives home the essence of what the filmmakers wanted to portray: a young man who came from very little who (with some help) was able to become a star.

I know you probably don't care that much about The Blind Side, but it's instructional because all of the important characters are

1. Alive
2. Well-documented through books, articles, media appearances/interviews, speaking engagements, etc.
3. Around at a time more-or-less analogous to our own

1 is very much not the case for the historical figures featured in Amadeus. 2 is somewhat true for Mozart, Salieri, the Emperor, and some of the other main characters, although it should be noted that "well-documented" for 1790 and 2010 are two very different things. 3 is also not true for Mozart, and this is possibly the most crucial point of all.

We know that Mozart had a sense of humour that many would find juvenile. There is, in fact, an entire Wikipedia page entitled "Mozart and Scatology," a delightful fact that I sometimes bring up at parties (I don't go to many parties). Some passages in his letters to his cousin Maria Anna would be seen as the height of comedy at a six year old's birthday party, like

Oh my ass burns like fire! what on earth is the meaning of this!—maybe muck wants to come out? yes, yes, muck, I know you, see you, taste you—and—what's this—is it possible? Ye Gods!—Oh ear of mine, are you deceiving me?—No, it's true—what a long and melancholic sound!

He also wrote multiple choral pieces with texts that discuss ass-licking and bed-pooping, which are actually quite nice. So yes, to a certain extent, Mozart had some of the silly sense of humour that is displayed in the movie.

However, it's pushed to the extreme to make a point, which I'll get to later. We do know that he was fond of making jokes, playing with words, and generally being a fun and funny guy. We don't really find the over-the-top, bordering on madness type of behaviour that the film depicts.

Another aspect of his movie persona that is somewhat close to real life is his genius. He did in fact often write out pieces without seeming to make many (or any) corrections/edits, like his oboe quartet, suggesting that he could hear and compose fairly complex pieces in his head. He composed his 36th Symphony in four days, on a stopover in the town of Linz (the local nobleman wanted a concert and Mozart didn't have suitable music with him). I wrote about another example of his purported genius in an answer about him hearing a piece and then writing it down, note-for-note.

He wasn't, though, quite the musical factory he is sometimes thought to be. He worked hard, and had his challenges like any other composer. Yes, often he ended up overcoming them with spectacular results. But he wasn't always a continuous fountain of music. He wrote to his father in July of 1778 that he was having difficulty writing an opera in French:

It is true that the devil himself invented their language, and I see the difficulties which all composers have found in it. But, in spite of this, I feel myself as able to surmount these difficulties as any one else. Indeed, when I sometimes think in my own mind that I may look on my opera as a certainty, I feel quite a fiery impulse within me, and tremble from head to foot, through the eager desire to teach the French more fully how to know, and value, and fear the Germans. Why is a great opera never intrusted to a Frenchman? Why is it always given to a foreigner? To me the most insupportable part of it will be the singers. Well, I am ready. I wish to avoid all strife, but if I am challenged I know how to defend myself. If it runs its course without a duel, I should prefer it, for I do not care to wrestle with dwarfs.

God grant that some change may soon come to pass! In the mean time I shall certainly not be deficient in industry, trouble, and labor. My hopes are centred on the winter, when every one returns from the country.

By the way, about that father. Leopold Mozart was a musician and composer himself, very good but not historically great. He raised Mozart as the consummate musician, teaching him at a very young age. Mozart was composing by 5, and spent much of his childhood touring around Europe, playing concerts with his father and sister. Leopold was supposedly a bit of a taskmaster, and certainly had high expectations and standards for his son. He was controlling, and often at odds with his strong-willed son as he grew up.

Mozart's early musical success and childhood spent performing often leads to parallels with the King of Pop, Michael Jackson. The two of them, robbed of a normal childhood, are seen as never having really been able to grown up. This is the "perpetual child" archetype, and it's one that forms the basis of the narrative of Amadeus.

(Continued...)