Hi Irishman,
I went to Zhangjiajie on my honeymoon this April. I wrote about it on my trip to China. It is beautiful. I went on a three day trip, taking in the Yellow Dragon caves, the fantastic cable car ride, walk down from the top, then the riverside walk. Rare trees, wild monkeys and rare birds. We didn't take a boat on the lake, but we didn't have time, but the views and the nature were truly spectacular. We used a Changsha travel agent, went there by bus and it cost 1400 yuan for me and my wife. You can also fly there or take the train. I hope the weather is better for you than it was for us on trhe first day. You really need the sky to be clear to get the best views from the top.