are you set on led lights? metal halide and sodium are much cheaper and will grow you 4 plants under a 400 watt. 600w is better, you can get these ballasts with multiple settings for bulb brightnnesses, 250w,400w and 600w all on the same ballast. so you start them on 250w, then grow and flower on 400w and finnish off under 600w.
just worth thinking about if heat isnt an issue or you have extraction fans