we will have to evaluate to determine if the system is worth rebuilding , most likely we can .

You can have a few issues with either a faulty valve or a gravity discharge damage to the lowest spray head on that watering zone of concern.

Most likely you have some sort of water leak , since most sprinkler systems run late at night or early morning a simple broken nozzle, lateral leak which is after the valve or a main water line suppling your valve could be the problem.

you can have a few issues there , faulty rain sensor, damage wiring , faulty master valve , faulty controller, main water supply damage .

you can have a few issues with several things with a faulty valve not opening , lateral leak , over nozzles with out the water supply allowed by the valve .

Yes there is several techniques in the irrigation industry that we can do to prevent unexpected water usage .

Yes

Yes

Yes