I also recommend you to start from the very beginning of the course.
Remember not to start saying: "Boys and girls, we are going to try a new method I've found on the internet to see if it works..." It's always better to say something like: "Well, here you are in Xth grade! Now you are ready for a new challenge..." and you present Whole Brain Teaching...
I also agree that you don't need to start with everything, but step by step; although if you feel comfortable enough, you can always go for all of it..
Best,
Edward