Without the Sony software, you won't be able to buy books from Sony or borrow library books. Any other books you purchase with DRM like from Borders or Kobo, you could download using ADE for Mac and then drag-and-drop to transfer or use calibre to transfer. Unfortunately ADE for Mac does not recognize the Sony ereaders so you can only use it to download the DRM'ed books and won't be able to use ADE to transfer the books.
Here is another suggestion that you might try. When you have uninstalled Reader Library, it's difficult to get a clean reinstall unless you follow the steps recommended in this link:
https://www.mobileread.com/forums/showthread.php?t=78921