Hi @aurelia thank you, I'm glad you've found this helpful!
There isn't really one answer for how zoomed in our out you should be. I wouldn't focus on the percent. That will all change depending on your screen size and canvas size. For instance, my canvas is built to 16.5" x 20.5" at 300 dpi. The scale percent is very small to see the whole image.
For different stages you'll probably want a different zoom percent. When thumbnailing, color, and initials lay ins for shapes and final color, I have it so I can see the whole canvas. This is because I want to see how the marks I'm making will effect the whole image. I'm also keeping in mind how most people will view the image. I really only zoom in further when I have to. I probably zoom in about as much as you see in the giants head close up, above in my first post. That would be when drawing faces or other small details. Same when drawing the people with the lantern. I will also keep zooming out to see how the new marks are effecting the image. I hope that gives you some idea?
Something cool to check out to get you in the mindset might be some impressionist paintings. Degas or Monet for example. When you look closely at their works it can be messy and sometimes look like nonsense squiggles, but when you stand 10 feet away, the whole image comes together. I think most art is meant to be viewed from a slight distance. This will change for picture books or phones, where people's eye will only be a few feet from the image. The scale might be similar to the impressionist paintings example, though.