i have 925 watts in total i have a 600 watt hps light 85-90,000 lm and 3 envirolights in a space thats much smaller tha yours jus in a wardrobe cupboard thing so i rekon youll be fine
as far as i know you cant really have too much light
just watch out for the heat... thats a killa if you have too much (like me)
and yea you will need more light for that space size (probably)