Well for one, the maximum width of an image Tapas will allow you to upload is 940 pixels, so 1600 is too wide. As to how your comic will look on a mobile screen, I personally like to have only one panel visible on the screen at any given time, so I make sure there's enough space between them to make this happen.
This is my guide on the general dimensions of a screen, I just make sure the panel fits within this pink box.

Here is a full scroll of one of my episodes, it's about 18 panels. This is before I put it in a slicer, so it should give you an idea of how a scrolling comic generally looks.
On Webtoon I consolidated this episode with others so it is even longer. That's the nice thing about scrolling comics, you can stack as many panels as you want because of the vertical format.
