Something I have always found interesting about the USSR is how a ''revolution of the proletariat'' (i.e. the people) so quickly and violently shifted to be centralized basically in the one figure of Stalin.
My understanding from reading on it is that there actually were elections in the beginning and all kinds of different party branches.
I can't really figure out how a system that was founded to put its power in the hands of the workers, in a matter of a few years became a dictatorship.
The idea of Marxism which is what the Lenin based his revolution on does call for the proletariat to rise up, but there was always an elite level during Lenin's lifetime. After Lenin's death Stalin essentially took power in and concentrated power in his person/office.
After the fall of the Russian Provisional Government during the October Revolution (1917) you don't see any elections as the Bolsheviks took power by force of arms. Before the revolution and abdication of Nicholas II you see elections to the Duma, but these were boycotted by some parties and attended by others. The party that eventually took power was the Bolsheviks which were a violent faction of the Mensheviks.
Marxism was an idea that had (in my mind) some utopian elements. This idea eventually interacted with human greed and the need for power. The answer to your third point is that the ideological foundation of the soviet union was deviating from its base ideology from the start. This is the reason that Marxism and Leninism are differentiated from each other. Stalinism is also seen as a separate system. Essentially human greed and the person of Stalin are responsible for a true dictatorship, though Lenin was no saint.
You could try looking at Stalin: The Murderous Career of the Red Tsar by Cawthorne, but there are many many quality books and articles about the atrocities that Stalin committed and about the soviet union in general.