Ur electric bill is gonna suck lol. and u should yeild about what ur guessing, maybe alittle bit less. But who knows. 4plants per light u can do more then that. 400wtt hps covers a 4x4 area. plus more plants = more buddddies. but then again u will be able to make trees with that room. so it might work out. Its all in your technique. If u have less pplants vegg longer and they will be bigger, or u can do abunch of smaller plants its your call.