Not an official support answer but read it elsewhere in these forums. For #1, the display only indicates ON when the cell is actually generating chlorine. The cell essentially always runs at full power (power levels aside) and the % you set it for is actually the % of time that it is on. Even at 40% it would still go OFF, just less frequently. If you wait long enough with it set at 10% you should see it go on and then cycle back off.

I can't answer #2

For #3 - even less "official" but the SWG superchlorinates in the cell so the ppm within the cell is actually well over 15ppm even under normal operating conditions. I can't imagine that shocking to 15ppm (which isn't an unusually high shock level) would have any negative effect whatsoever.