I'm going to Beijing, Shanghai, suzhou, Hangzhou and Wuzi. I want to go to Xian to see the Cotta Soldiers

According to my experience, eight days are not enough to cover all the places you mentioned. It need at least 7 days to visit Beijing, Xian and Shanghai. If you want to cover them all, at least 10 days are needed.

As for the transportation, you can take flights or high speed trains from Beijing to Xian and Xian to Shanghai. It is also very convenient to travel between Shanghai, Suzhou, Hangzhou and Wuxi by bullet trains.