1. It costs 30$ to get a copyright
2. The leanth of time varies with the copyright
3. Minors can get a copyright, and the Copyright Office can give registrations to the minors, however state laws may regulate the business dealings, with copyrights owned by minors.
4. It depends on what you wont to copyright.
5. Yes, you can be sued for using someone else�s work
6. You have to get the owner of the copyright and ask him.