Went to China twice this year, was in Beijing, Shanghai, Guangzhou, Zhuhai, Xiamen, and Hangzhou. For Lego go to Shanghai and look for the 80101 and 80102 New Year sets, they had both in stock when I was there end of August (they are only sold in Asia). Easist Lego store to find is near People's Square metro stop, walk along Nanjing Road east back towards the big river. The other store is at enterance to Shanghai Disney, but smaller.
See the Bund (locals call it Waitan), the river walk in central Shanghai, closest metro stop is Nanjing Road East, one stop east of Peoples Square, so easy to both Lego store and the Bund. Great views, especially at night. Metro is easy to use, hardest part is buying a metro card or ticket, machines sell tickets, but see a booth with a person to get a card (20 Yuan plus whatever you load on it, 40 Yuan should do, so about $9).
You are also close to Hangzhou, go walk around the West Lake, very pretty if it's not raining. Buy your train tickets in advance if you can, the high speed trains sell out 1-2 days ahead and all that is left if the slow trains. To enter the main train stations you have show a passort, and they will scan your baggage entering every train/metro station.
China was one of the toughest places for me to visit (been to 36 countries) because of the language barrier and Google maps doesn't work well. If you have a local to guide or escort you it's a lot easier.
This site is full of great info: https://www.travelchinaguide.com/cityguides/