You should probably read about a hundred pages a day. That will get you through the troll arc in about a week. For the whole adventure, it'll take you about a month.
As for Aradia beating Vriska up just because, yeah, that's quite possible. She said she was sorry for making her boyfriend kill her. Some people just can't forgive.
It makes Aradia a more interesting character if she did it because she wanted to. If it was part of some timeline management thing, she still didn't have a choice in the matter, even if it's something she'd really like to do, and that's not really satisfying. But if there's no timeline management attached, she made a choice, the first one in a while. It's an improvement, however small of a one, over being the unquestioning servant of anybody who will give her orders.
And you want to talk about forgiveness? How about we talk about gratitude? Vriska had that soulbot made as a gift, and how does Aradia say thanks? By killing the person who had it made! Talk about ungrateful.
However, if the other timelines were doomed, doesn't the rift make the prime timeline doomed as well?
Well, yes. But it's apparently the best option of infinitely many, all much less favorable.
The trolls are probably at the end of the things they can do themselves to fix it. So their only recourse is to troll the people who did it and hope
they can fix it somehow.