Feferi asking the Horror Terrors to make the dream bubbles occurs very early in the timeline of the Furthest Ring. Time works differently there so events that seem to occur at a certain time to us may have come about differently in the Furthest Ring. For example, Rose and Dave creating the Green Sun occurred extremely early in the timeline of the Furthest Ring because once you enter the Furthest Ring time begins to shift in odd ways. So from Feferi’s perspective the dream bubbles are new but to the ghosts living in there, the bubbles have always been around.

Yes, although they’re called yellow-green bloods by Kankri.

Yes. 

Yes, he asked her to mediate between him and Sollux. 

There are only two fuchsia bloods in existence at a time, the Condesce and the heiress. So if you’re writing about one of the heiresses before Feferi then go for it. Also there’s a link to the FAQ in the description which you can see on mobile.

2

Here. 

Yes, Rose and Dave flew to the center of Derse’s moon during [S] Cascade. 

Homestuck is a big sprawling comic but honestly many of these questions wouldn’t even need to be asked if they just searched the blog or checked the FAQ.