2. doesn't matter, the waiting is based on your priority date, which will not change no matter where you are (even out of US).
3. 274a.12.c(9) is only for I-485 filers. And if you are eligible to file I-485 (if priority date is up), then you can get EAD on that basis. however, you may try F1-OPT (c(3) basis) since you are F1, your international student advisor knows how to do that very well, and they need to do I-538 for you too (they know how to do it).