Well, the good news (as you probably know) is that you can travel extremely efficiently in China, and there are lots of night buses and trains. It's possible to jump from Kashgar to Hotan to Kucha to Turpan to Dunhuang using overnight buses (and since I couldn't find budget places that allowed foreigners in Hotan and Kucha—or in Jiayuguan—I had to rely on those buses). Some arrive very early and/or don't let you get a full night's sleep, but they're very doable. If I had to do things over again I would have spent more time in Xinjiang, but that's because I felt the 'stans were a bit of a letdown after Xinjiang—coming in the opposite direction you'll have a better idea if you want to linger.
Regardless, I think it's possible to see everywhere you listed. There are lots of buses between Xining and Tongren, and one or two between Tongren and Xiahe, so this is possible.
I've also found that the wikitravel entries for China are generally much better than they are for Central Asia.
Anyway, I think this is a workable schedule:
- 2 days doing Tashkurgan and KKH
- 1 day in Hotan (night bus from Kashgar)
- 1 day in Kucha (night bus from Hotan)
- 1 or 2 days in Turpan (night bus from Kucha)
- 2 days in Dunhuang (night bus from Turpan)
- 1 day in Jiayuguan (night train or bus from Dunhuang, but only 5 hours or so)
- 1 day in Zhangye (sorry, didn't do, but I hear the mountains are much less impressive in person and very touristy... I took a night bus from Lanzhou to Jiayuguan)
- 2 or 3 days in Xining
- 2 days in Tongren (day buses for this region may mean you want/need extra time)
- 2 days in Xiahe
- 2 days in Langmusi
- 1 or 2 days in Linxia/Bingling Si/Lanzhou (night train to Xian)
That's 19 days, giving you a couple of days to make necessary adjustments. It's a bit quick—sometimes out of necessity—but possible.
I'm happy that you've found my blog useful, and the crappiness of LP China (especially the sections written by Michael Kohn) are part of the reason I included lots of detail for some places (like Hotan). If you visit the Atlas silk workshop in Hotan and spot a gorgeous girl working in the showroom, you can repay me by sending me a picture of her.
Enjoy your trip!