@Gawain According to your edit, so yes the camera size is the final resolution. Is what people see and the size of the video. You always have to plan according to that.
Also a pixel is a pixel it’s the minimal unit that makes the structure of an image. Hence it cannot be divided to create more (not in Pencil2D at least). When you zoom in you will get to see the real pixels that make the image because you’re “closer”. So, to avoid unnecessary pixel-ly look when you zoom in, you have to plan which frames are the ones that you are going to zoom into so the drawing can be tailored for that size. Normally if you create a bigger drawing, you’d use that as your guide.
So for example. Say you have a 400 x 400 camera frame. That means the final video will be 400 by 400. Now, lets say you have a drawing that is 800 by 800. The camera will only frame about half of that image anytime. So in order to frame the whole picture you have to zoom out. However if you zoom in, half the current size (200% zoom) you will inevitably see pixels. In such case you have to plan that Your 100% zoom will always frame the closest possible size for your drawing. And the rest of camera work will occur at a zoomed out state.
Its difficult to put it into words. Another practical example. Just imagine you have a face, and the smallest part you want to show is an eye. So you have to make sure that the Eye is visible at 100% zoom, hence making it necessary that the face be really big. And so if you have to show the whole face most of the time you will remain zoomed-out, and when you have to zoom in, you will never go beyond 100%