I'm not Keu Cha so you probably don't care what I have to say, but with something this big you either start with that image you have in your mind and grow it outward from there, or just top left hand corner.
Outstanding drawing! Is it a double-page spread..? Looks like a single landscape-format sheet of paper, not two preprinted blue artboards taped in the middle. Soft or hard lead pencil..? Wooden or mechanical..? Or a lead holder..? Seems to me it's a direct sketch on a single sheet, not a light-table clean-up.
It's one page and I use B lead in lead holder. I don't have a light table big enough so I have to bite the bullet and draw away. Sometimes it works, other times I scrap and try again. Practice makes perfect.