Good that you caved to the presure of everyone, I agree its so much better to watch the whole thing in one go. Great deal on the DVDs.
It wont take long it finish them, you can watch one series in a one or two depending on time or one a night until the event but you'll get hooked, my guess at least disc a night.
My fav's are Out of Might, Out of Sight (season 1), Phases, (season 2), Band Candy (Season 3), Hush (Season 4), Family (Season 5), Once more with Feeling and Tabula Rasa and Villians (Season 6) and Him (Season 7). Most of them except Villians are filler episode, more fun than impact.