October Holiday, please help me.

We are planning a holiday to China in October, I know there is a week of Chinese holiday at the beginning of October. Will this effect our trip in any way? What is the weather like in October? Is it too cold to visit beaches? We are planning on going from Hong Kong - Beijing - Xian - Zhangjiajie - Hong Kong. Is there anything you can recommend seeing at any of these places besides normal tourist attractions?
Thanks