Personally, I'd do no more than 1/4 turn at a time. It's too easy to find you've overshot things by the time you get all the way around the wheel. It seems to keep other aspects of true/tension more consistent.
I find a slow, methodical approach gets me to the end of the journey faster.

NDS usually will have a greater effect due to the angle of the spokes.
Unless the DS is already at very high tension, I don't loosen it.