I'll jump in for the clothing. Every period movie makes a good number of sacrifices on accuracy due to cost, availability/time, and most importantly the overall "image" of the film. This is why it's very easy to know when a period movie was filmed- the aesthetics of the current day rub off. I'm not going to go through and list all of the things "wrong" with it, that would be too much. For the most part, they really exaggerated what would have been popular in 1984.

The ladies gowns are very curved and bosom accentuating in a way they would not have been in the 18th century. The desired shape was an inverted cone, which does lift the chest, but less "wonderbra" shape. The trims aren't overly exaggerated, but the proportions are off. The men's suits are decent, though there's some excessive lace ruffles going on. The embroidery and trimmings are fairly on-par for about 20 years earlier. As for the wigs, they aren't oversized, but they are very fake. They would have been wearing human hair or very often styling their own with hair pieces. Hair was pomaded and powdered for both haircare and styling, though powdering to the point of white (or pastels if you preferred) was very optional.

The point of the movie was to show Mozart as a bit of a rock star in a very opulent and over-the-top (but antiquated) court. Here is an actual portrait of Mozart for comparison. Another portrait shows him in a very plain brown suit. That realism just wouldn't have much impact on screen, especially not when the character is meant to be a very dramatic rock star.