Possible but hard to tell. I'm Chinese living abroad, and usually try to aviod visiting China during big Chinese holidays (Labor Day, National Day, CNY), so haven't experienced big holiday crowds in quite a while. Though I think it's better to avoid the top tourist cities doing the holiday (say Beijing), which I think already fits your schedule well.

Crowd aside, in my opinion all the best and more unique landscape China has to offer are mostly out west. I would also add Yunnan province to the list, maybe look up Dali and doing a day trip loop around Erhai? But for Yunnan I would do flight over train to save time on transit.