The showed size of the material can be changed utilizing CSS, however in the event that you do this the picture is scaled during delivering to fit the styled size, which can make the last designs delivering wind up being mutilated.
I am sure the dpi would not have anything to do with it. It would be the pixel size, because screen resolution is in pixels. If you have 4096x2160 in pixels the DPI at 300 13.653x7.2 inches. If that is what you have, then you can sketch everything out on a smaller canvas. It means you will have larger brushes to work with if you need to brush in large areas, and when you want to go with the finish you enlarge it from 100 DPI to 300 DPI. Anything in the distance that you painted will not need anything else done. You just spend more time on things that is in focus. Where the edge looks blurry, because you added more pixels to work with you create a sharper edge by painting more details.
Sketching is important, and it helps to build the scene as you develop the art into higher quality work.
Canvas sizes can be anything you want them to be, because if you draw a map, and need more space to add to the map, you can add more with canvas space. If you want to add more details, then you can enlarge the image.
DPI helps you multiply, because a canvas of 4096x2160 at 100 dpi is 40.96x21.60 inches. You just move the decimal over, because it is like 100%. Changing it to 3 times larger by changing the DPI is easy.
If you get into making every pixel look good, the quality of you art would look great, and you can zoom in to make details people don't notice larger, and the details are extra fine.