Respuesta :
Im not very familiar with WebToons, but smaller panels should be fine. I do suggest setting up a test toon so that you can see whether or not WebToons will take smaller panels. Its best to check before putting in work and having to resize/redo it all.
Answer:
it mainly depends on what platform you are reading it on, though I would recommend making the panel 800x1280 because that is the one that fits the panel size for each device universally.
Explanation: