1: Does the Olifant Mk 1A tank have night vision like in real life?
Yes and laser range-finder
+ How much of the night vision stuff (IR searchlight, flares, light levels) actually effect AI LOS?
As in real life
2: Are Laser range finders factored into the aiming of tanks (olifant, chieftain) that have them / can they be used by player if future playable tanks have them?
Yes of course
Chiftain don't have laser range-finder, It uses a strange system with a machine gun sighting (in game too)

.
3: Can helicopters be shot down / will they be destroyable in future?
Yes
4: How can I move crew to other seats? <- This one's really important I keep losing battles because my tank loses its loader or gunner.
Only auto by AI. Sit to another tank and AI can be move crew.
5: Can the Chieftain be modded playable if the gun sight reticles were made like Steel Fury?
Theoretically yes