The first thing that needs to be done, is setting aside a suitable place for growing. This is actually a large portion of the obstacles you’ll need to overcome.

Hopefully you’ll size the room according to how much light you’ll be supplying and below is a rough guide:

400 watts = 3×3
600 watts = 4×4
1,000 watts = 5×5

There are several mathematical formulas floating around for properly sizing your exhaust.Yes you can have many lights in one room. You’ll also need ventilation and exhaust. Besides ventilation and exhaust, you should plan on air cooling your light. At the very least, a glass shield helps alot. No glass shield or air cooling is a recipe for disaster. Besides exhausting your grow room, you’ll need some intakes for fresh air to be bought in from outside the room. If you are using a 6″ exhaust, you want double that on intake.

Here is one:
Take your lights wattage, multiply by 3.2 and divide by the cfm of your exhaust fan.
400 watts x 3.2 / 500 cfm = 2.56 degrees above ambient temp is where your grow rooms temp will be.

More is always better. The sole purpose of an exhaust is not to only expel the heat, but also to replenish the depleted co2 in the room. You’ll also need an oscillating fan in the grow room.

It will take some experimentation on your part to find out what combination of fans works best.

On the note of experimentation, and opinions for that matter, you’ll find growers to be very opinionated people. We love to experiment, and we all believe our way is the only way. This is so false it’s not even funny. There are 1000′s of ways to successfully grow the plant. Remember it is a weed after all. If the advice one grower gives you, does not feel comfortable, or does not fit your growing style, seek out some more advice.