Milk

The recent spoiler stream confirmed that Moonlight is Shai, I think. Besides, Moonlight literally calls herself Shai as an Elantrian. Presumably, she is unpracticed with the Essence Mark because she can't power it.

Mraize actually mentions this in Chapter 13 of RoW, saying that Radiants and spren (among others) "cannot travel farther than Ashyn or Braize." Not sure about the ten gas giants in the Rosharan System.

Not really? We see two full Skybreakers with twenty squires while Szeth is training, so seven squires isn't all that much.

That would be the case if they were all Rosharan. I think it's more likely that only one of them is a full Radiant—who doesn't even need to be a Rosharan—and the rest are squires. I doubt that the Ghostbloods got that many highspren to join.

Skybreakers can choose to follow the codes of a criminal organization. Besides, Nale's group of Skybreakers is also an underground organization.

Bravery is much closer to Valor than Odium or Cultivation, though.

Arguably, pre-Shattering Investiture could still have Intent. Spren created by Adonalsium were largely of Cultivation, for example, although Cultivation wasn't separate from Ado until the Shattering. Besides, the Investiture of/from the Dawnshard would match its Intent (in Rysn's case, Change), no?

Forgery changes one's Spiritual self; a Spiritual change will have some level of descending consequences to the Cognitive and Physical, I think.

We don't know whether the Evil occured at the same time as Ambition's death, actually; it might have been unrelated. I think that her Splintering affected the Shades more than the Homeland. I don't think that we know when Nazh left Threnody, so he may be behind on its traditions or its state.

I doubt it; spren, highstorms, and other manifestations of Investiture existed pre-Shattering.

This same WoB actually suggests that Seons are not bound by the same restrictions as spren. Perhaps it's due to the Shards not actively Investing in the planet? Shades can leave Threnody, according to Secret History.

I don't think this is particularly relevant. Breaths are of Endowment; they can leave Nalthis freely, so I don't think Vasher would face any big trouble. Furthermore, Seons are able to leave Sel, and they are pretty similar to CSs.

Ashravan can't go Worldhopping, since his Soulstamp would fail outside Sel, but Hemalurgy would work. From what I can tell, there are two possible states that Ashravan could be in. 1) His soul has left the body, and the Forgery is essentially a more impressive Lifeless. 2) His soul is still Connected to the body, but the Resealers couldn't heal the brain to the Cognitive/Spiritual aspect because Selish healing is bad. I have no idea what'd happen with better healing. Returned are Cognitive Shadows, and Ashravan is not one. You could see CSs as artificial souls, though, if you believe that they are bits of Investiture fit into the mold of a deceased person.

DS, ch. 19: “There are songs . . .” Cord said. “From long ago. Of when this . . . Command came through the pool.” It entered Roshar through Cultivation's Perpendicularity, apparently. I don't think that's particularly relevant here; the perpendicularity is located within Patji, an avatar of Autonomy. Perhaps a more mysterious one is Yolen's?

Yes, the initials of the books form a ketek. (It's specifically divisible into five parts) Brandon has a tentative title for Book 5; Knights of Woeful Truth, which would be shortened to KoWT.