The Renoir we see for most of the game with the nice ass suit is a creation of the Paintress, correct?
Correct, the curator who upgrades our weapons is the real Renoir.
Who the fuck are “The Writers”? Did they start the fire that killed Verso?
Some other magical negros who have beef with the painters for whatever unexplained reason.
What’s the significance of the Gormage and why does the Paintress need to kill everyone of a certain age? Is it just to count the passage of time since Verso died?
The paintress didn't at all. The one causing the gommage was Renoir, the real Renoir who is killing the people to get his wife to leave the painting. As more people die to Nevrons(creations of Clea) their Chroma gets trapped unable to return to Aline, the paintress weakening her allowing Renoir to gommage more and more people. The number is a waring to the people that they're the ones going to be next.