Yes can file both at the same time.. If your case is strong then it is fine to apply for both at the same time. Your lawyer (if you have one) can also advice on this as well. I-140 is not garunteed to be approved thus will be wise to wait for it to get approved and file for 485 unless you feel very confident about the case and also seek advice from your lawyer or an immigration expert. Premium processing can also be considered for extra $1000 but for I-140, and please note that they say it takes 14 days which doesn't mean that the case will be approved within that time. You will get some kind of decision within that time frame. All cases are not same and time frame varies. And again try o consult an expert on this matter since rules/laws change. Good Luck..