.....I) The resolution they are made and displayed in, from 128, 256 or 512
.....III) Whether or not you are willing to recolour the items and how much it would cost.
A) Using copyrighted work without proven owner consent (plagiarism) is strictly forbidden, and you must credit all other artists work. In other words, if you're selling c/p textures or images post a link to the original image.