Over time, I have purchased and experienced pretty much all Videos and DVD available:
- Marc Savoy Gospel according to Marc (and the other one)
- Dirk Powell Vol I & II
- Steve Riley
- Wilson Savoy
Like you, I started with the Dirk Powell. I would say get Vol II to continue building a solid foundation. From there, the Steve Riley or Wilson Savoy (which are both intermediary/advance) would be a natural segue in terms of style and complexity. The two Marc Savoy are not very good in terms of teaching methods, but amazing to watch.
You will find that learning on an Ariette (which is what I did too) si going the hard way, but once you graduate to a good quality box, you will be much faster and better. It's a little bit like the athletes who train with extra weights... I've attached a link to my interpretation of Valse de 99, the very first song I learned from the DP video a couple of years ago.
Lache pas la patate!
I agree that the 2 DP Vids are the way to start. Next Steve's Vid and Wilson's are terrific. There is a lot of material on both but I think Wilson's lesson on triplets is key to really opening up the fingerboard and helps get that cajun sound. It is also a favorite lick of the modern Zydeco players and gets a nice syncopation in there. Here is my 2 cents. Always play the scale over and over just like DP shows you in the beginning. This will train your ear so you will always get the octave without thinking about it. Then try to pick out tunes and you will automatically play them in octaves. Add the embellishments that you feel and voila, you have your own arrangement. I think it is helpful to learn the chords, 1, 4, 5 in both the push and pull keys and then in the F position and the D position. Play along with CD's and just chug some background using the bass buttons to get that chank a chank going. Also, a key move is to get the G going (on a C box) in both the push and pull. This will help you keep that box going in and out in that endless stream of notes that to my ear really define this music. Steve Riley's version of Flammes D'Enfer comes to mind. That lick that he does really opens the box to your own improvisation once you get it down.