B) Key tech is the photo-cathode that "amplifies" light. That thing is heavily restricted because it's a bunch of material science state secrets. Too much light will damage the tube by pushing the electrons past where they can return to zero.
C) Depends on generation of NVG and type.
There are a few types:
1) Light amplification (passive) - First gen, needs moonlight, bulky as fuck
1a) Active amplification has an infared (usually) or low intensity light shine around you.
2) Out of Band near IR - Heavily restricted, great for defensive duty/counter sniper (Very little reflection in other NVG)
3) Digital - power intesinve and feedback delay, cheap and heavy as fuck.
4) Thermal - Mainly firefighting use, GL getting a high res one. Higher ones heavily restricted
5) Fusion - Thermal + image amp. If you find high quality in the civilian world expect FBI to knock your door. Chinese ones better than the US ones in certain aspects