Since you have space of 3x4=12 your 400hps is not enough for 50watt/sqft....you need 600watt for that.....if you don't have good ventilation avoid using the 1000MH...it will cause heat problems even on top of the 400hps.....i think you can do your growing even with the 400hps with descent results(33.33watt/sqft).....best of all though is to get a 600watt hps....