1. Not much, but maybe a lot. Depends on how rich or poor you are. 1-10m per crystal. Also depending on the shard.
2. People told me: they can be healed through standard healing spells.
3. Depends on what you are fighting. They are said to be about as strong as a nightmare.
4. No. But rumours have it after transferral they can become bonded again - to the new owner.