NATS (Nissan anti theft system) is your immobiliser. The chip within your key (red square) is picked up to tell the ECU to basically work. If you tried to start the car without this key (IE a re-cut one with no chip) it wouldn't work as NATS would not start the engine, it would turn over but not fire. The light is there to basically tell anyone thinking of nicking your car that it has an immobiliser. Or sometimes they are used to show you have an alarm.
Yes Clock is always on
The pedal can become stiff, if you open the engine bay, udnerneath the airbox you will find the throttle body. To the right hand side of this is where the throttle cable attaches. This can sometimes stiffen up and a little wd40 should sort that out.
