Here is my situation...
I am about to install a one piece neo-angle shower in a corner with 2 exterior walls. I have determined that this may be a problem in the future if any work needs to be done on the plumbing behind the shower. There would be no way to access pipes except to remove shower or cut through exterior of house. Two things that would be major headaches.
How big of a problem am I getting myself into?
Keep in mind space is very limited and using the exterior walls are the only way the shower will fit.
I wouldn't worry about it. Moen and Delta and others make repair plates if the valve needs to be replaced. Just make sure if you are in a cold climate area to insulate the walls and pipes well.
CO and Smoke detectors save lives. Know your limitations and when to get a PROFESSIONAL. Your life and others may depend on it. Volunteer to be a local Fireman or EMT and help your community.