If you want the easiest non-wifi method - use Calibre.
Forget the Sony s/ware, new or old !
Plug in and install Calibre.
Just choose your book, buy/get your download file, the drag and drop into Calibre Library, send to device, and you're there.
And it's not buggy at all - which I have found the latest (but not the very latest , that's coming, we all hope) version to be, a tad.
And the version you down load is set-up for T1.