Hi Am an Indian passport holder working in japan , i have a couple of questions to be answered

My sister lives in Shangai, and i would like to visit Shangai in December So

a) What is invitation letter from China Travel Agency? Is it OK if my Sister sends me a Invitation letter ?
b) I have an Japan Resident Register Card (Alien Card). SO do i need to take re entry permit to japan again? (FYI , In Japan Resident Register Card , a person can enter japan again as re entry system was abolished in Jun 2012)
c) Where can i get Application Form for Visa? Download or Visit Consulate?
d) Do i need to fill Visa Application Form OR Supplementary Visa Application Form? (FYI, Am an Indian , applying visa from Japan)
e) I will be staying in My sisters house. So do i need to produce Hotel Reservation?