I don't think folder names are used by calibre to assign metadata.
Under
preferences>adding books you have several options and can test the regex against a file name.
I am not a regex person. I just import books and then download metadata and usually the default regex (9/10) works for me.
I have read data from the file contents checked and swap author firstname and lastname checked although I may on occasion uncheck one or both.
I actually pay little attention to the naming convention used on books before I import them as the metadata in my case is generally taken from the file contents.
But in a text file with no metadata embedded
Author LN, Author FN - series xx -title works for me with the way my preferences are set.
Smith,John - myseries 07 - title for book.txt
(?P<author>[^_-]+) -?\s*(?P<series>[^_0-9-]*)(?P<series_index>[0-9]*)\s*-\s*(?P<title>[^_].+) ?
I think it is easier to rename the books inside calibre after importing them. But that is me.
The bulk edit metadata dialogue has a swap author title function and the individual edit has one as well. In the individual edit metadata dialogue you can also view the book if the title is not apparent. and the download metadata is pretty configurable and works pretty good.
If you do want to rename all of your books first, and I can see reasons for wanting to do this, then make sure read data from the file contents is unchecked or the result may be unexpected.
Sorry to be so wordy
Helen