I suppose you know that, you should file 485 for your wife before yours is approved. Once you got your GC, you'll need file 130 for your wife, and that 's a long wait, you wouldn't want to do that. And if you wait to submit 485 later, you'll need an employment verification letter to support that you are in similar or the same position or field as the one that you submitted for 140. For finger print for 485, I don't think you can do that in China. Somebody correct me if I'm wrong. For leaving for 2 years, lawyers suggest not to leave longer than 6 months, there is a form 131 using for this purpose, but when you come back, you will be asked to prove the necessity to enter the US. Search this topic on google, you'll find a lot of information.