How big of closet? If it is less than 3x3x7 the 600 will be a bit much, but you can dim it so could be cool. Make sure you air cool with a quality fan, a cheap one will not be enough in such a small space.
I used a cheap fan to air cool a 250hps in my old closet grow. I just made buckets similar to rain forest systems( rain forest 6 from general hydroponics). They fit six clones in a three gallon bucket, so 12 plants in a 18"x32"x40" wardrobe closet. Each bucket harvested about 4oz, so 4oz a month, I cycled the harvests so I got one bucket a month. I had a smaller cabinet for a mother and clones. I would highly recommend the rain forest bucket in your scenario or do like I did buy one then copy design and made another one for yourself. It was a pretty bitching system.
I tried it with a 400 watter and got the same kind of weight, but bud was fluffy and not as good because the 400 just put off to much heat to control and that was in a bigger closet that was 3 foot x 2 1/2 x 4 foot. I just couldn't kept it ventilated.
All that in my room, still living with the parents
they never noticed a thing! Damn kids! That was in 2003, not many people were hip to the scene back then.
PS, I tried dirt back then to, but with space restrictions you're better off going with hydro. Dirt plants want to take way to long and you can't flower out a soil plant after 1 or even 2 weeks of veg like you can in dro. They need 3 or 4 wks to make it worth it. IMO.
