I've seen mods that make your character look like Lightning from Final Fantasy, or like characters from anime. Is there a guide to making character models like that? Do they have to be made from scratch or can you import the character models from somewhere else? (I know nothing of 3d modeling >_<)

think you would be better off asking in the modding section and think you were suppose to. Also why don't you just look for the type of skin you want, someone may have already made it. Try the skyrim nexus.

This does indeed belong in the modding section. And you'll find no shortage of anime themed mods on the nexus, I've had to sift through dozens of them trying to find proper lore-friendly mods.