That was his dreamself. Vriska woke him up, then he flew home. This seems pretty obvious, even without reading the pesterlogs...
No one does, last we saw of her.
He's probably the hardest to follow, as we've seen future (casual shirt) Dave, and past (MC suit) Dave. Currently he was making the money to send to Past Terezi, so she traces the money and finds the kids in the first place. Money seems to be for fraymotifs, we don't know exactly what they are, but they're things to do with fighting.
Dream Jade died. Real Jade current has a giant fuck ass meteor about to crash into her home. This is... really fucking obvious. All the kids had meteors, and you can see it at the end of Descend.
>this "demon" that's plaguing the trolls came from out of fucking nowhere to me (and may be explained later but if it already was I totally missed this somehow)
It's Lord English. We don't know who he is (hints point to Jack) he's a universe eating demon. He came from the rift at the end of Hivebent; the one that denied the trolls their reward (our universe)
>Then Derse & Prospit get destroyed by said "demon" that came from nowhere, this essentially kills everyone's dreamselves I think.
>What's everyone even trying to do at this point?
John is saving Jade, Dave was fucking around with Terezi, Rose is trying to break the game, Jade is being a narcoleptic derp. Trolls are trying to troll the kids and/or find a way to live.
Seriously, this stuff is mostly explicitly said in-comic.