Ben nye is your friend for the Green skin, as are green tights (Welovecolors has some).
I was painted green once for a skit from Elphaba from Wicked. I used a small cake of Ben Nye color and it didn't even take the whole cake. Of course always use a sealer when using body make-up.
Now costume wise it looks great! We can't really say the cape so I can't say anything about that but the one thing I did notice was the gold clasp on the belt looks too flat. Is it just a piece of fabric? I'd suggest using a 3d object. It would make it look more real. I personally, would use half of a Fillable Ornament
. If you paint the inside of it then put some puffy foam (It's used to fill gaps between pipes and walls and such, you can find it at a hardware store) it will seal the paint in and then put a safety pin on it or hot glue it to the belt it should look a bit more realistic. (:
Over all this is a great start! (: