All excellent advice.
So what's your comfort level for snugging the screws? I usually drive them in gently until they stop, check to make sure the binding is perfectly flat to the ski by holding the ski up to a light, then turn any of the screws more as needed to pull the binding flat (toe pieces are cake, but there always seems to be 1 stubborn screw on heel pieces for whatever reason). At that point, I alternate over the screws in a star pattern and try to give them a teeny bit of extra oomph to snug down (generally about 1/16 of a turn or less).
For me, it's entirely a feel thing. Basically, there's a point at which the ski is "telling me to stop" and I stop. But the screws are snug--no question about that.
A good experiment you can do, is to torque the screws until they are snug. Then, wait a while. Then unscrew them. If it's too easy to unscrew, then you should torque them more. But basically, I torque them until the screw serious starts to resist my torquing--and then I stop.
So far, I've only mounted tyrolia railflex plates, so I dunno if it's the same for regular bindings. But I think it should be. I don't worry about the binding being flat to the ski. Once all the screws are torqued, the binding is always flat. My problem is that the binding isn't always centered perfectly. That's why I will purposely screw in one screw completely tightly before all others--so I can get the binding perfectly centered on the ski. I am usually still off by half a mm or so, but it's not really significant.