Def not gonna need a new window. i say 200A alt and a group 34 optima or the largest kinetik you can fit under the hood, big 3, 1/0 wiring (thought thats probably more than 400, but you wont have to spend what your budget it for subs. save the 250, you wont need a new window. did you want new or used subs/amps?
i dont care bout the amp but im just goning to order the BTL with the cooling system and would like to have enough power to make it show what its capable of doing