So to come back : I did Shanghai (3 nights) - Hangzhoun(4 nights) - Nanjing (2 nights) - Shanghai (2 nights). No side trip really on top of that. I had a blast, everything went really smoothly (apps, payment, Didi, trains, public transport), people were helpful when a mini App needed a local phone number and always proactively found solutions so I could order food/drinks/get a ticket. Only place where payment did not work at first trial was a tea shop in Hangzhou.
Highlights were some out off the beaten track water town in Pudong, walking in the tea fields of Longjing and a sunset on the walls at Nanjing. On the other hand the West Lake was overrated in my opinion. It was great early morning but after 8:30 AM the place is a zoo.

China has changed a lot , specially when i compared to my visit of Xi’an in 2016. Quite amazing to see the speed of construction. I hope the free visa get extended one more year.