travel from Tashkent to Beijing via Turpan, Dunhuang, Chengdu, Xian

Hi
I am a little confused...do I take the train from Tashkent to Turpan or fly? And then travel through China by rail. Dunhuang to Chengdu seems to be a long rie, more than 23 hrs, so could you suggest a city to break journey for a couple of days? I prefer to travel overnight by rail but not for more than 10-15 hrs.
Thanks