Yes. United States law recognizes lower receivers as the definitive part of a “firearm” (the part that loads magazines and houses the trigger). This is why Lower Receivers have serial numbers and Upper Receivers do not. This means that Upper Receivers, stripped or assembled, are not considered firearms or part of a firearm until attached to or stored with a compatible lower receiver. This makes it perfectly legal to purchase any Upper Receiver with a full auto bolt carrier group.
No. Since the Upper receiver is not considered a firearm by definition, they do not require transfer through a FFL holder. These items can be shipped directly to your preferred shipping address.