In reality a surname including a prefix seeming to allude to nobility like "von", "van", "de" or "af" is not possible to take as a new name in Sweden. So "von Sternberg" wouldn't have been possible to take. Artistic freedom, of course, but still factually incorrect.
Danny Saucedo, a well-known Swedish singer, is said to have had a relationship with Mahmods girlfriend just a couple of years earlier. However, in real life Danny Saucedo had a long relationship with another well-known Swedish singer, Molly Sandén.
The story is set in 2016, since a huge part of the plot is that the 30 million SEK that Mahmod/Sebastian has are in old 500 SEK bills that will be exchanged to new bills in a short period of time. However, the Volvo XC60 that Mahmoud/Sebastian drives is a model that wasn't available before 2018.
Mahmod and his friends find 90 million SEK and divide them so that each if them get 30 million. Soon afterwards Mahmod spends money on buying a car and buying a house (among other things). A house, at least, would cost him some millions (in Stockholm, that would be about 10 millions or so), still at the end of the movie he claims to have all the 30 million left.
At the beginning of the movie, Mahmod and his two friends find 90 million SEK and split the money between them, so that each one of them get 30 million. Soon after, he buys a house (worth at least 10 million SEK), a car, rents an office etc (not to mention other living costs). However, at the end of the movie, he still has all of the 30 million as If he never touched them, payed for anything or bought anything.
The odds that Isabell wouldn't had never seen "Sebastian" without his blue contact lenses are rather impossible, since most lenses are visible if you look person's eyes close enough, and contact lenses needs to be removed before going to sleep.