Is this scenario technically possible? Sure. Is it likely. I find the odds of that extremely slim.
"All his generals" are like a handful of them, all infantry. One of the misunderstandings around Bolsonaro is that people think most of he top brass supports him, which is not the case at all. He is a grunt. An infantry captain who started his career as a grunt. He is popular with infantry conscripts and infantry NCOs. But the elite of the Brazilian Army, the professional divisions such as Electronic Warfare, Intelligence, Armored/Mechanized, Engineering, Air Cavalry, etc... despises him, as they view him as a brute and simpleton. His popularity is even lower with the Airforce and the Navy (the most prestigious branch of the Brazilian military). Unlike say, Argentina, the practices of torture, oppression, assassination, where always controversial within the Brazilian military. As much so that in the early 70s, the army hardliners were removed from power by the army moderates, exactly because they could not stomach the abuse, the tortures and the assassinations. All political prisoners and guerrillas were freed and given full amnesty (Dilma and my own father among them), and the gradual process of returning to a normal constitutional democracy was defined as goal by the army rulers.
So thugs like Bolsonaro have very little support among the top brass, which today is made up mostly by moderates. Even General Geisel, who ruled Brazil from 1974 until 1979, who lead the process of return to a normal democracy and is considered within the army as the model of what a Brazilian general should be, referred to Bolsonaro on his memoir as a "piece of shit" and that is a good reflection of how he is viewed across the board. So it is not like he has lots of generals to pick from.
Also, even if he did, most appointees need to be approved by Congress. So does the increased number of judges. Does Bolsonaro has the majority of Congress? No, he does not.
It is important to remember that both Lula and Dilma tried the same approach of populating the executive and supreme court with their puppets, and even with a much broader Congressional base than Bolsonaro has today, they failed. And to add on top of that, Bolsonaro has been in congress as a representative for 30 years and has not been able to get a single one of his bills passed. Not one, in 30 years. He was also unable to get a single mainstream politician or political figure to agree to be his vice-president. Even the most rabid anti-PT figures, like Janaina Pascual, refused to share the ticket with him. So he had to rely on an obscure pariah retired infantry general to be his vice-president, after his 7 previous choices rejected his invitation. That speaks volumes about this lacking ability to form alliances and coalitions. Hitler, Mussolini and even Chavez where skilled politicians who were able to build coalitions and bring different groups together. Bolsonaro has never been able to display such ability, even on this election, where he ran as an outsider without any broad political coalition behind him.
So unless he is able to completely transform himself, I don't see him accomplishing this "soft coup" that you speak of.
