I have had 2 Kobos, the Clara and now an H2O2. Series management on both is a piece of cake. I use the Calibre plugin mentioned, and it handles both sideloaded and store-bought ebooks. If I buy a book as a new addition to a series that I created on Calibre and sideloaded on to my Kobo, the Kobo itself will add the new book to the collection.