Travelling from Changsha to Zhangjiajie or Wulingyuan by bus

I would like to compare travelling by train and by bus to ZJJ or Wulingyuan so i have some questions about bus as the following;
1) Travelling from Changsha to ZJJ or Wulingyuan by bus, it will take how many hours?
2) Where i can get the bus?
3) There are more bus from Changsha to ZJJ comparing from Changsha to Wulingyuan?
4) If we hire taxi from Changsha to ZJJ, how much dose it cost (estimate)?


Thank you very much,