Are you going to compete? If so, what kind? You may not need 3 batteries for 4 second burps, but I would probably reccomend getting atleast 1 extra. It's also going to blow your budget out of the water with wiring and battey costs. Furthermore, are you considering any type of a front stage? It will be quite difficult to hear more than bass with 7200 watts. Have you considered costs of sound deadener. I belive you have quite an ambitious project going on here.