Need Help finding the best route between different cities

Dear Sir,
I am travelling between Guilin, to zhangjiajie to FengHuan finally to Xian, My questions is:
1) What are the minimum number of days that are enough to see Zhangjiajie and also FengHuan. P.S: I want to spend one day in the Avatar mountains and I consider them separate cities with separate hostels.
2) is it better to go from Guilin to Zhangjiajie then FengHuan then Xian or Guilin then FengHuan then Zhanjiajie then Xian.
3) Could you please tell me how to go (Trains and buses only, no planes) after answering question number two.
Thanks alot for your help !!