There are at least three ways to get from Shenzhen to Guilin / Yangshuo.

Flights to Guilin take an hour, but schedule isn't great and you have to take into account travel to the airport and check in times.

You can catch an overnight train to Guilin, although it is quite a long journey.

In my opinion, the best way is the overnight sleeper bus from Shenzhen.

See http://www.yangers.com/ for more details.

For flights see elong.net - maybe possible to go up to Xi'an

You need not stay Shenzhenovernight, you can fly from Shenzhen to Guilin directly, this is the best option. Guilin Yangshuo is very nice place for holidays as it has relaxed atmosphere, if you want to see more and enjoy more in this area, 4 or even over 5 nights is required, Guilin for 2 nights, Yangshuo for 3 nights. You can visit www.guilinprivatetours.com for more info.

When you arrive in Guilin you should stay in Guilin for one or 2 nights, as Guilin is in the middle between Rice Terraces and Yangshuo. The first night you stay in Guilin, the night day visit Rice Terraces, Day 2, Li River Cruise, around 1 pm get to Yangshuo, then you can enjoy the countryside, you will see real China here. Have a nice trip.

Take flights from Shenzhen to Guilin can save your time. There are many flights from Shenzhen to Guilin, so you can choose the one best for your time.

For the places you want to visit, 3 to 4 days is ok in Guilin. If time is limited you can only stay for 3 nights and if time is enough you can stay 4 or more nights. One or two nights in Guilin and one nights in Longji and you can still stay one or two nights in Yanghsuo

2 days in Xi'an is enough for warriors.

Thanks everyone for your responses

Look at www.yangers.com/Shenzhen_to_Yangshuo.htm for good information on this route. I would probably prefer the overnight bus because it goes direct, and you won't have to waste time messing about airports and delayed flights.