One of the first things you should consider is air exchange. You're going to need a fan that can replace the air in your closet in at least 5 minutes. And since you're growing in a closet, it's almost a certainty that you'll have to use an air cooled hood. It's the only way you'll be able to keep the temperature manageable, not to mention that you won't be able to use bigger than a 400w light (maybe a 600 if your closet is a good size like a walk-in). Your money should first go to a good extractor, and then a good air cooled hood.