shouldn't need a heater in the grow box as heat from the lights should be sufficient. you should keep the lights on 24/7 until you are ready to start flowering because for a marijuana plant in the vegetative state does not need any night periods as older plants do. as far as your fans go, i keep mine on all during the day but off at night. seems to work great. plant lots of seeds and keep the strongest few of them depending on your space.