I work with pencils and inks on paper so maybe it won't be very useful, but for my webcomic Purple Boudoir, I always go with A3 paper (29.7 x 42cm = 11.7 × 16.5inches), and a 600dpi scan for the colors. So my files are usually really big and heavy haha!
Working big is always the best, as a lot of mistakes will sort of "disappear" when the page is shrunk down (you've already noticed what the opposite does). But then you need to learn the amount of details you want to pour in your art. When I started using that size, I used to add way WAY too much stuff in my panels, just because the paper was big and it felt empty otherwise. But then when the smaller page would be ready, all of these details would either disappear or make the page unreadable.
Maybe you could try playing around with different kind and sizes of panels, and see what fits you and your style the best? 