2. In first stage, file I-140, which it's to evaluate if you're qualified to immigrate U.S., there is no difference of where you live. You can even live in China. Once I-140 approved, the second stage is mainly to wait for visa quota to be assigned. If you live in U.S. you have two choices:
A: file I-485 ajust status to GC
B: file immigrant visa petition in your birth/home country
If you live outside the U.S. you only have B: choice.
Normally B: is fast than A: For eample, A: in Vermont center takes 2 and half year but B: in Montreal takes 9-15 months. But go with A: you'll get some I-485 benefit, which you can apply EAD and AP.
Is this clear?