I will be taking a bullet train from Tongren to Changsha.

Well, first of all, no bullet train runs from Tongren to CS. You can only take the normal speed train.
The CS Railway Station is about 25 km (15.5 miles) from Huanghua International Airport and 10 km (6.2 miles) from the South Railway Station. The surrounding transportation is convenient.
Would you mind provide some scenic areas that you wanna to visit? In this way, I can find the exact distance among the railway station and these scenic spots. :)