These usually take longer (in part because the environmental pieces tend to be smaller). For example the Super-X drawing took about 3 weeks, while the accompanying illustration took about 10 days.
Buddy, I can't do your work for you. That's up to you.
Well they're literally arthropod-vertebrate hybrids, which is fundamentally unlikely, to say the least. I'm sure you could evolve a similar, smaller scale, predator by natural means though, maybe from an annelid ancestor or something.
Maybe, but by the present day most, if not all, have already been destroyed (by time, battle, or other various reasons). Creations of a similar nature will appear, though. The Cosmos were a very isolated empire (both geographically and policy-wise) and it's questionable that either the Kilaaks or Infant People even knew they existed.
The Skull Island civilization... will be a story for another day.