You ask about shading shoes. If you are going to shade the sprite, shade it constantly. When you are standing in a dark room, and somebody turns on a light, do your shoes remain hidden in the dark? No, they are revealed by where the light hits them.
Keep the dark outline? Well, one interesting thing to think about here is actually using the color of the outline to further depict the shading. Use a darker outline on dark edges, and a lighter outline on the highlighted areas. Remember, this is just one solution to your problem. Use your best judgement.
From 1x, I cannot see thumbs. I would say that because you aren't going for a very realistic person that a detail like thumbs is something that's better left for imagination on the viewer's part.