It seems that in whichever subfolder/parent folder I create new columns with metadata, these colomns are also shown in each parent and subfolder. Can I disable this behaviour so that each level in the folder structure can have it's own metadata set (= columns)?
Library columns are not specific to a folder and are available at all folder levels of the library. You can however restrict the use of columns by using content types. Content types can represent all sorts of content including types of document and folders.