i dont know if there is a better position for the lockout during storage, but wouldnt think so. and i dont really know why you'd ever need to turn it on while on the fly.
preload allows you to adjust the suspension to your weight. you dont want it too soft as it will use up the travel. to hard and, well, the suspension is too hard/stiff.
rebound is how fast (or slow) it takes the coil in your fork to return to its original shape.
im guessing the knob on the bottom is for damping, or how fast (or slow) the coil compresses.