What time of year are you planning? That might make some difference in recommendations and order of destinations.

Other thoughts:
--For 30 days, it seems like a bit much, you'd be spending a lot of that time in airports or other intercity transport. There may be some connections that are better/more reliable by train. Again, when are you planning your visit?
--Shenzhen and Guangzhou I'd deprioritize. Given that there are some more important ways to spend time in/near some of the other places on your list. You can pick them up when you next go to HK Disneyland.
--Sanya I'd deprioritize. It's just simply no comparison to the SE Asian beaches. And besides being out of the way, it's relatively expensive to get to.
--Be very strong in your desire to visit Zhangjiajie--including it always adds a layer of hiccup and time-snarfing logistics as there are limited flights in/out to limited places, and other options in/out are ponderous.

--Are you a hiker, or just prefer quick looks around a scenic area without too much effort (be honest)? Depending on answer, might change the timing factors.

--Your itinerary is not well-fleshed out yet. For instance, nobody (with any sense) goes to Lijiang and out again without seeing something else of the wonderful surrounding area. It's just pointless to do so. That means allotting an appropriate number of days. When you start really doing a day-by-day and including logistics, you'll see how fast 30 days gets eaten up.

--If you must start/end in Beijing, making some sort of general circle like you propose usually makes sense. But I'm not convinced your order of visit is the optimum one.

--Cost: 5000 GBP?!? Jeez, I could do 30 days for this itinerary in half of that amount or less, flying everywhere, paying lots of high entry fees, and staying in very comfortable places. But without knowing your travel style particularly for accommodations, not easy to advise you on this. Accommodation cost will be the biggest single variable.