1 - Don't do it, you can break your tendons and ligaments. The stretch should be gentle and you should feel pleasure, not pain.
2 - What's the maximum amount of work you are willing to put on it? There are no rules set in stone. You reap what you sow. It also depends on how advanced you were on previous lives. Do not dwell on the event. Focus on the process.
3 - It means you breathe it out of your body instead of keeping the energy of the element inside. Practice the foundation meditation before playing around with the elements.