The rightsholder would be unlikely to take action.
A copyright is granted to the person that created it. A user name is not considered a proper identification of a person. You will have to use your legal name to register the copyright.
No, copying and pasting is copyright though.
Yes.
It means that if you copy something copyright and don't give it its props (or credit) you will be sued
I would expect that everyone using the internet has at some time or another done something that would be considered copyright infringement, whether they knew it or not. That would be about 28% of the world population, or nearly two billion people.
It depends on whether you have the right or not. If you control the copyright to something (i.e., you drew/painted/wrote it), you have the exclusive right to copy it or authorize others to do so. If you do not control the copyright, you need an exemption in the law or permission from the copyright holder.
No, it should not. If you wrote something, you own the copyright on it. All you need in order to assert that copyright is proof that you wrote something.
Copyright protection is automatic, so it actually takes effort not to copyright something you create. That being said, copyright allows the creator to ascribe value do and potentially derive income from their creation.
There is no such thing as "un-copyright". Something is either copyrighted or not. If it is copyrighted, then the copyright eventually expires, making it public domain.
A business holding a copyright on something can prevent others from abusing it, and make money by licensing its use.
You need to write something original and then publish it, applying the copyright mark, the date and your name. Copyright protection is automatic.
Dozens, if not hundreds. Every time you create something new, it is automatically protected by copyright. Doodle a picture of a cat, you have copyright. Take a picture with your phone, you have copyright. Record yourself making up a song, you have copyright.