I would like to travel to Zhangjiajie at middle of may 2014

Hi,
1. Is there possible if we would like to explore zzj by our own? Is the place that we should visit can be arrived by taxi or bus inside zjj?
2. If we would like to hire a tourguide at there can we hire on the spot? How much it will be?
3. About the ticket fees roughly is how much yah? For 3 days entrance.
4. The places must visit in zjj and can we just spend 4 days, is that enough?
Thanks so much.