I used to do all this advance preparation - until I found out that you can get a visa in about 24 hours in HKG for China. There is a travel agency in the Sheraton (plus many others) that gets them for me every time and have never had an issue - applying is a breeze - they even take your picture! They take your passport for that time so be prepared. If I were OP I would start with a trip to HKG - spend a few days there - get your visa, and then fly to Shanghai - see two of the worlds amazing cities in one trip!

EDIT - It is much more expensive this way - IIRC about $250 per visa...