21-Day China Itinerary – Recommandation needed

Hi everyone,

I'm planning a 21-day trip to China in September, focused on culture, architecture, and traditional cities (not so much into nature or hiking, but we walk a lot daily).

Planned route: Beijing – Datong – Pingyao – Xi’an – Guilin – Yangshuo – Zhangjiajie – Furong – Fenghuang – Hangzhou or Nanjing – Suzhou – Shanghai – Beijing

Is this itinerary realistic? Would you add or remove any cities? Between Hangzhou and Nanjing, which would you choose and why?

Thank you in advance for your help!