If you have a window in the attic get yourself a inline fan so it sucks freshair into your grow room,this fresh air will help with your plants yellowing problem youll also need to extract with another fan,you can put your lights on a timer if you want,personally i do it manually,just make sure you got a rely contactor for your 600 before plugging a timer in,try read as much as you can,get your enviroment sorted first and take it from there,good luck.

Baldy.