Just been there recently, like two weeks ago.
Two nights in Zhangjiajie, then bus it to Guilin - get there very early or book ahead for the Li river cruise - 8am to book and pay up front at CIT, cost 300Y for a bamboo boat - forget the big boat as it costs 400Y and takes all day - 2 hrs on a bamboo plus a short stop is enough. They make a quick stop for loo and drinks and some food. Finish at Xingping - lovely village, but take the bus back - included in tour - to Yangshou, spend two nights, the full day spend hiking, party at night. My travel partner did not want to stay so we ended up goingback to Guilin, so I will defo go back to Yangshou. Google Lonely Planet for hotels as good ones are few.
You can always take a bus back to Guilin - 30Y, 1 hr.
note, take the soft sleeper overnight to shenzen - costs 444Y for soft, do not take the hard sleeper - 295Y is not worth it unless you are extremely exhausted that you pass out immediately in a deep sleep, have heavy duty earplugs, and can handle ciggie smoke for 11 hrs in your couchette.
I am sooo glad I booked at least a day in advance for the soft sleeper, as you have a quieter carriage, bkf is provided for 10Y but after seeing the chef cook eggs with a fag in the other hand, I forwent. Boiling water is avail all night sotake a mug with some teabags or coffee sachets, and pot noodles.
Night train leaves Guilin about 8:30 - 9pm - times change so always get there no later than 30 mins beforehand.