Let me start with the first question: all those chords in bars 9 and 10 iv -> ii -> V7 -> i cadence in c# minor. This cadence adds the sharps that would change e minor to E Major, so it feels like a lift to E major, landing on its relative minor, c#.
There are some similarities here. In bar 9-11 we moved from e-minor to c#-minor, down a minor 3rd. In bar 18-19, that's happening again: c# minor moving down a minor third again to b♭. But the difference is that in 9-11, the cadence strongly led to the NEW key, while in 18-19, it very strongly leads to the old key, c#. This isn't really a modulation at all-- it's quite jarring, and deliberately so.
The same thing happens again in bars 25-27: a big set-up for a landing on e♭ minor, but instead jumping down to c minor. So in each of those cases, they are landing a minor 3rd down from where you'd expect.
Imagine a movie trailer with a lot of sudden cut scenes. This is kind of the musical equivalent of that-- a series of musical cut scenes.
So what holds it together? The constant repetition of a couple of rhythmic / melodic devices in the right hand: first a 3-3-2 division of 8, and later, then a kind of buhhhh-buh-buh-buhhhh in bar 11, which has a 6/8 feel and can be counted 1, (2)-and-a, 1, (2)-and-a. . . In both rhythmic devices, the scales mostly move in a very similar way: holllld-step-step-holllllld.