Well done ! I've been to Manzanar and you've captured it perfectly. Everyone should go and see it first-hand.

"Glass sandwiches" are good for holding curly negatives. Consider using glass from an old flat bed scanner (everyone has several of those, right ?) because it probably already has anti-reflective qualities.

Consider visiting some of the "smaller" cities, for example Guilin, Qingdao, or Changsha. www.tripadvisor.com has good overviews of these and other cities. The megacities that you mention are interesting and fun but can be overwhelming. The smaller cities have retained more Chinese flavor and friendliness. And there's lots of non-urban parts of China to see, for example: the "Avatar" mountains, https://www.youtube.com/watch?v=RDoMYr7b44M and great photo opportunities: https://www.cnn.com/travel/article/china-beautiful-places/index.html. Plan to ride the G trains between the cities...almost 200mph, always on time, and a lot more comfortable than flying. This guy can tell you all about the trains: https://www.seat61.com/China.htm. I've been to China 36 times...I can't wait for Trip #37. No matter where you go, you will have fun. You have chosen your next vacation well !