You're definitely going about this the right way. You have an excellent set of gear in the 3 600's + 1 ST-E3 (I personally went with 4 600's). Now, all you have to do is add stands and modifiers AS YOU NEED THEM, to place the 600's and tailor their output to achieve the lighting effects you desire.
I think creative vision is the most important piece of "equipment" for effective lighting. I've seen too many photogs invest in a bunch of gear, without knowing what they want to achieve with it, or even how to use it, really. Far better to have a look in mind, and then acquire gear as needed to realize your vision.
(And +1 on the recommendations for air-cushioned stands!)