I would personally layout the map on the 18x12. I would bring the crop marks into CC3, and then when I go to export the PDF for home use I would export a rectangular selection that is only the 17x11 area and when needed for the printers I could do a full export which would include the bleed area and crop marks. This would cut out having to mess with many tools outside of CC3.

What you have works though, I would never blame somebody for not breaking what already works.

My name is Cole Hinkel (DoubleDouble). I have a bachelor's in Game Design and am familiar with a wide variety of the tools involved for graphics and programming in general.

My portfolio is currently empty, that will be remedied soon.

You can contact me by PM here or email me at colerhinkel@gmail.com

Be sure to include some details about what you are looking for and maybe even some examples in the style you are looking for. I look forward to bringing your world, city, or encounter to life.

I also immediately knew that these were cliffs, myself.

Did you know Sue did an analysis of how she did the cliffs on that map? https://rpgmaps.profantasy.com/orde-on-the-rock-map-analysis/