I need help as to what visa I will need as this is imperative when the time comes.

Hi there I am booked on a cruise in 2015 from Singapore to Shanghai on Royal Caribbean I make several stops in China. We first arrive in Hong Kong on March 11, 2015 where we spend the night then arriving in Xiamen on March 13th, my cruise then terminates in Shanghai on March 15th. I am aware that I do no need one for Hong Kong as Americans can visit there up to 90 days, I do not plan to stay that long. Also Im visiting Ho Chi Minh(phu My) Vietnam in this cruise, the cruise line stated they provide a visa service onboard to visa Vietnam. This does not apply to China as I will have to apply for that one on my own. It would help if someone could give me some clear information to this subject as I have never visited PRC which Im looking forward to. Please email me back with your thoughts. I also live in Philadelphia PA, which nearest office to apply for a Chinese one. As Im traveling in March of 2015 when is the best time to apply and going about this? Also my passport does not expire until April 2016.