When you say the sustainiac "doesn't sound quite right" can you elaborate? Or maybe post a video of what you mean?
What Hector said is true, and as long as the strings don't touch the pickup when fretted you should be in good shape. The closer the sustainiac is to the strings the faster it will affect them, sometimes having it just far enough away so you have some delay in effect can be musically beneficial.
As for the floyd, my personal rule of thumb is for the strings to be low enough to the neck for comfort, but when I bend one I don't want the strings all getting stuck under my finger, which will happen if it is too low. (Conversely, if they are too high they will go over my finger, and that doesn't feel right either).
IMPORTANT: If you go about changing the action setting of the floyd, (which involves tightening or loosening the screws on which the floyd rests) You MUST loosen the tension of the strings before turning the screws. If you rotate those screws with full tension of the strings, the screws will dig into, and dull the blades of the floyd which in turn makes it fall out of tune very quickly and unavoidably. (Useless guitar at that point)
If you have any more questions, I'll do my best to help!