Just have time to look at your scans but not to address all of your content. Hope the following helps somewhat:
Your scans reveal you could probably have a chin wing AND a chin shield; BOTH. That is to say you don't have an overly high sloped mandibular border that would make it more difficult for them to cut through all the way to the back of the jaw as to lower the border of it (for which a graft from the hip would be needed). Although your scans don't show where the nerve is, there does look like there is enough room for them to avoid it while doing the chin wing cut in order to 'drop down' the border of mandible.
The chin shield comes into play when in addition to the 'drop down' to the mandibular border, the mandibular border is displaced FORWARD to advance it or even if you no drop down but just forward advancement. In the case of forward advancement of the mandibular border, a chin shield would be used to camouflage the lip to chin GROOVE that could become MORE accentuated with forward advancement of the mandibular border. Hence, that's why I say you could have BOTH if you so elected to do so. If all you wanted to do was to camouflage your overly acute chin groove, you could get only the chin shield. However, if you elected to get the chin wing to advance your mandible border forward, you would probably need to get the shield along with it.