tourist visa questions

I am traveling around Southeast Asia, China and Japan for five months (july until december) this year and had some questions regarding a Chinese tourist visa.
Firstly, if I am in China and wish to travel into and out of Hong Kong once during my time in China would I require a single- or double-entry tourist visa?
What form of travel documents does the embassy require, (flight details etc)?
How many days would it take to process? And must the visa application by made and collected in person?

Thank you for your help.