moihasceboko WebP images cannot be loaded in the Spine Editor, so you will need to convert them to PNG or JPEG for animation. However, you can export to WebP when exporting from the Spine Editor, so the final textures can be in WebP format.
The optimal image size depends on several factors, so it is difficult to provide specific guidance based only on these samples. Many users animate much larger images in Spine, but the appropriate size is determined by the intended use—for example, if you need to zoom in on a specific area during animation, very large images are necessary to avoid visible pixelation. On the other hand, if the final display size is relatively small, using excessively large images only increases loading time without benefit. For this reason, we cannot give precise recommendations without knowing the final display method.
One important note: as long as the aspect ratio is unchanged, you can replace the images of an already animated skeleton with higher- or lower-resolution versions. This is described in the Scale section of the Import page in the user guide:
https://esotericsoftware.com/spine-import#Scale
