I mean using couchsurfing specifically for getting to know locals, not crashing at their places! Most of them either live with their parents or in student dorms until they marry anyways. But especially the "internationally minded" guys and girls are usually very eager to get to know westerners and actively search on couchsurfing for meetups (no actual couchsurfing involved). Just post a message with the dates you are there and that you are looking for a local to show you around and grab some food with you. I would be surprised if you wouldn't get at least a couple of responses. Probably also a lot more insightful than hanging around with other expats/tourists or factory people all the time
M50 is a common design tip, but for my taste it tries a bit too hard to be artisanal and hipsterish. Still worth a look if you have the time, but don't expect something gamechanging.
Is it your first time in China? If yes, then you probably will be very busy just exploring side alleys. You can still see a lot of the "old china" (in the parts where buildings usually don't have more than two stories and look shabby) where life is happening still mainly on the streets. I could do that for hours especially when I just arrived Shanghai. The smells and sounds and impressions are mesmerizing. MUCH more interesting than touristy places like Xintiandi or Tianzifang which are nice and clean... but that's about it. The density of Starbucks and pizza restaurants in those areas is pretty alarming
Another thing you should put on your list is hanging out in a chinese walmart or carrefour. It's just fascinating how different the shopping experience is compared to any western supermarket. Prepare for life fish, turtles and a ton of stuff you never heard of. It gives a pretty good impression of what the average chinese middle class consumes (food or non-food items). Oh, and they also usually sell "clean" and safe to eat versions of some of the street food mentioned before, in case you want to spare your stomach. You can just google them.
If you are into electronics or gadgets you also should check out one of the huge electronic malls they have. Usually massive 5-6 floor buildings with houndreds of small independent shops that do normal retail, repair, online business and wholesale at the same time in the same place. Your chance to see thousands of boxes filled with computers, tablets, phones, spare parts and weird gadgets at once. And in the middle of it all a bunch of chinese dudes fixing phones. The hectic and chaotic athmosphere is pretty representative of Chinas current tech industry I would say.
They are relatively easy to google.
Oh, and a general tip: Get a VPN BEFORE you enter the country. Yes, you will need one, the internet is THAT bad in China without one, trust me. Even if you stay just a few days. Those few bucks will be worth it