There isn't a perfect amount, depends on the length of activity, amount of sweat, etc. Also remember that sweat isn't water only, lots of electrolytes. 20-64 ounces is appropriate.

Depends on body weight. Depends on sport. Depends on heat and humidity. They are formulas you can look up to calculate it. You should be drinking throughout your activity.

Till you're no longer thirsty.

I am a firm believer that a healthy body self regulates regarding the basic needs including hydration. I think it is common sense to hydrate with water or sports fluids at a moderate pace, but not to guzzle them down. Our bodies thirst mechanism is very reliable unless it is not operating normally due to illness or disease.

You should be hydrating with water before, during, and after sports participation. Your urine should like similar to water if you are drinking/hydrating sufficiently. Urine should not be a dark yellow - if it is, you are behind on your hydration/water intake.