After some elimination of unwanted elements, I have the line art ready for coloring. I drawn in Adobe Photoshop in a AO size canvas. Initially I was thinking to use Adobe Illustrator, which is flexible for resizing in vector graphics, but I still go for Photoshop; I will jump around among graphic apps depend on the subject matters.
The next step will be coloring and refining the necessary elements, then do test print for color accuracy and mounting on few finished sizes. Color accuracy part is my true headache due to different color profiles on so many different brand of large format printers in the market. I have to look into this issue more in order to have the closest results.