Hi cubefree
Yes, you are free to copy any Content Type to make your own. However, if you really want to customise then you should look at copying the Field Types as they are the data fields. Content Types are essentially containers of the containers of the data, if you understand what I mean. Whilst you can add, modify or delete the fields within them, by using and modifying (without copying) the supplied field types you are also changing the fields in the content types that use them.
I am not sure why the uncategorized Section and Category are hidden. It is obviously good to have organisation of content/articles, but there may be more of a reason for that. I am sure Bes or Saba will be able to say why.
Peter