Since I replied to another post from you about a replacement case, I'm going to assume that this is another post about the same phone. Since you are now talking about two major parts for the same phone, I would definitely suggest getting a bricked for-parts-only iPhone 5 to do the repairs. Even if the phone is iCloud locked, the back case and camera would still be useable for your phone, and you'll have the comfort of using OEM parts. You could also keep the camera module in the for-parts-only case to lessen the chance of getting dust in the camera module's space between the case and the module.
Also, since you were talking about the outer case, the outer lens is part of the case. In the iPhone 5, the case has a sapphire lens. With third-party cases, you don't have a guarantee of the new case having this protective sapphire lens unless they state otherwise.