3x3 is not that large, if you are doing 12 plants i would suggest flowering them after only 1 week of veg, kind of SOG style. Otherwise you will be VERY overgrown.

1000w might be a bit much for 3x3. I would suggest a 600w max for that size space. anything 400w and above is going to require air cooling.

i have 2 400w lights in my 5x3x6 space and it's very appropriate. They are air cooled and cover the area perfectly.

What kind of system are you using (Soil? Hydro? what kind of Hydro?)

Skeet.