16 nights and Zhangjiajie, China

You do not have enough time in Beijing. 3 days to do the main sights, 4 days if you want to start to get off the beaten track and appreciate the city/culture/history. If you are arriving in the afternoon of the 14th, you should really be departing on the evening of the 18th to do it justice.

2 days in Xi'an is fine. Not sure if you want to stop in Pingyao along the way.

You definitely do not need 4 days in Zhangjiajie and 2 days in transport to/from it.

You can easily fly from Xi'an to Zhangjiajie airport in 90 minutes, which probably makes sense given your time constraints and your desire to see it. I wouldnt spend more than 2-3 nights in Zhangjiajie though, 2 days in the park is enough, 3 days if you really love it.

Guilin is a transit hub, I think you want to go to Yangshuo(not Yuangzou or Yangzhou). I would try to spend more than 2 days there. It's not a wow you sight, it's a place to relax and try to glimpse slow rural life(although it is very touristy these days). If you only stay for 2 days, all you will see is the tourist development and touts.

1 day in Guangzhou is fine. No need for more there.

I think it's a very reasonable concept. But you're traveling in busy season and you may find that things like train tickets on the ideal trains are sold out. I'm going to assume that you are ending in Guangzhou because you already have a (nonrefundable) ticket booked on the 30th to Bangkok. So we'll run with that. Modify a bit and be willing to use flights.
14th Fly to Beijing
15-18th Beijing. You need more time than you've allocated. Night of 18th, book an overnight sleeper train on the Z43, soft sleeper is available and it's a good train.
19th-20th Xi'an. This is enough. Evening of the 20th, FLY to Zhangjiajie (airport code DYG). Right now if you go to www.ctrip.com there's a special for RMB 502, jump on this and book right now. Trust me, this is the connection to ZJJ that you want to do, not overland.

21st-23rd Zhangjiajie full days. Note that the Glass Bridge requires reservation so get to Beijing and look further into that. I'd split the ZJJ time as 2 days Wulingyuan Park, 1 days Glass Bridge and Grand Canyon.
24th Tianmen Mountain (adjacent to ZJJ city) for most of the day. Then overnight sleeper train to Liujiang. Right now soft and hard sleepers are still available on the K747 dep 16:28 and hard sleepers only on the T281 dep 19:14. On balance, I'd go for the T281 since it gives you the full day for Tianmen, stops less during the night, and arrives at a better time. This is a critical link and I'd book it asap.

25th Arrive Liujiang early. This is a new outlying station for Liuzhou city. Get a taxi to get you from Liujiang to Liuzhou rail station, then take a Liuzhou-Guilin fast train which is only an hour and not expensive. Should be able to buy this as a walk-up for next available, or buy in Beijing. Should be in Guilin by 10:00, at which point you can go to Rice Terraces or to Yangshuo.
26-29th Guilin/Yangshuo/Terraces area. You can decide how to split your time, but I'd minimize Guilin city. I'd get a fast train ticket 2nd class for the evening of the 29th from Guilin to Guangzhou. These tickets are selling out fast so I'd snap up something now or when you get to Beijing. There are also a few seats left for evening fast trains from Yangshuo (actually station is in Xingping) to GZ. Overnight 29th in Guangzhou.

30th Depart for Bangkok. Note: if your flight is later in the afternoon or evening of the 30th, you can do fast train from Guilin to Guangzhou this morning.

Train ticketing. Do it now or make it the first thing to do when you arrive in Beijing. You can go to any train ticket office (not necessarily at a rail station) and buy the tickets you need. RMB 5 surcharge per ticket, no big deal. Don't forget to take your passports.

This time of year can be rainy in the south. I'd stay further up north: Beijing, Wutaishan, Pingyao, Xi'an and Huashan. Maybe add Datong or Luoyang or Chengde if one interests you. As an additional advantage, there's much less travel involved.

Hi all

I woke up this morning and the first thing I thought about was my itinerary with a feeling of panic and then I grabbed by iPad to see if anyone had replied! Thank you all, so, so much. I did have a think about the weather and decided to go with it as I really want to see these places, thank you though. In relation to my planning, I booked my flight as suggested as soon as reading it. And after a 3 hour delay (sitting on a plane with no internet!) leaving Hon Kong I have just finished booking all trains. I've decided to plan and plan for this leg of my travels and save the spontaneity for another time! The only things to go now are deciding my time in Yangzhou (sorry for my previous spelling) and ZJJ park. If you have time, it would be lovely to hear about ZJJ in relation to staying inside the park or outside and using a guide or not? I quite understand if you do not have time though, you have given lots. Once again thank you, I feel like I am actually looking forward to travelling again, funny how things can become do daunting when feeling the pressure!!

"The only things to go now are deciding my time in Yangzhou (sorry for my previous spelling) and ZJJ park."

So you're heading to Yangzhou not Yangshuo? Please be very careful when making online bookings!

Yangzhou and Yangshuo are two completely different places, but I think it's pretty clear from the original context that he is talking about Yangshuo.

ZJJ: you can't legally stay inside the park, stay in the village of Wulingyuan which is adjacent to the park gates, not in the city of Zhangjiajie.

Of course, but I wouldn't be surprised if the OP's booked a room online in Yangzhou! Point is, we're not just being pedantic when insisting on proper Pinyin. Carelessness can have real consequences.

Of course, but I wouldn't be surprised if the OP's booked a room online in Yangzhou! Point is, we're not just being pedantic when insisting on proper Pinyin. Carelessness can have real consequences.

I know people who have made serious errors with train tickets, only to arrive in a strange town the next morning.

Sorry all, Yangshou. I couldn't make out how I made an error on my second email as I checked the spelling. Typing this have just realised predictive text has changed it! Thank you all again.