Okay first... awww thats cute! You should post a pic of the hedghog
Now I'm no genius on this but I can say the castor oil is one of the ingredients you want to keep since it acts as a "humectant by attracting and retaining moisturity to the skin."
You can go with cocoa butter but it is different from shea. "Cocoa butter lays down a protective layer that holds moisturity to the skin, making it a good skin softner." Cocoa is also much harder and less stickier than shea butter, plus it smells delicious!
Instead of the petroleum I would probably go with olive oil as the base since..."olive oil attracts external moisture, holds the moisture close to the skin, and forms a breathable film to prevent loss of internal moisture." It also does not interfere with your skins natural functions. Just so you know shea butter also does not inhibit skins natural functions.
And I got my quotes from The Soapmakers Companion by Susan Miller Cavitch just so you know.
So I would look into recipes for body butters/scrubs on the tutorial link and maybe use olive oil, castor oil, cocoa butter and sugar. Someone more experienced will have to answer your other questions, because I have no idea what the gigantic scientific words are!