Hello, I am going to be traveling to China at the end of June 2010. I have a passport issued in MN therefore I have to go to the Chicago Embassy to apply for my visa. However, I can not go in person but will be asking a friend to present my application form.

I am wondering if I should give her any other documentation besides my passport and properly filled out visa application form with picture.
I have not bought my ticket to China yet so I could not have her present that, but I will be staying with Chinese friends (who are citizens of China) while I am there.
Would it be a good idea to have them write an invitation letter for me to present with the visa application?
Should the letter be written in English or Chinese?