Lovely name! I think spellings Kalisto, Callisto, and Calisto would also work, and nicknames Kalli/Kali, Kal, Kalla, Listo, Liss, and Lissy would all be cute. Very elegant and versatile name :D.
I think Kallisto is a cool name. I like the spelling and meaning. Although it does sound somewhat masculine, I think it could work for either gender. In-fact, I've always liked girl names that end in “o”. I also like “Kal/Kali” and “Listo” for nicknames. Overall, I think Kallisto is a nice name.