A 2: I don't know the answer to your TA/RA questions. You may have to ask someone else. Why do you need to include your TA/RA experience anyway since you obviously have work experience in China?
A 3: Just leave the photos inside the package. Do NOT stick it onto the application form.
A 4: Given the amount of time taken between the first letter and the second letter (8months appx), you will be in the country of residence for one year. Therefore,I would recommend you to go ahead and apply through Buffalo. The worst scenario is they return your application, but I doubt they will.
A 5. I certainly understand your concern. But that's a risk you have to take regardless. If you did work there, your ex-employer would have to admit such fact. Who knows you may not be selected for background screening?
Good luck to you, Pal.