Well if your talking 5 gallon buckets, that's a nice amount of space for plants roots to grow. You could veg for a lot longer then 30 days if you wanted to, thus bigger plants. With a 600 hps, maybe you should go with nine plants. nine buckets placed in a square, 3 buckets long 3 buckets wide kinda thing. You would probably only be using up an area of 3.5 feet x 3.5 feet. And you could veg those plants for probably at least couple months before setting them into flower. And as far as yeild goes, thats a BIG variable, but anytime I try to anticipate yeild I usually aim for at least 1 ounce per plant. But yeild depends on size of plants, and the longer you veg the bigger the yeild. hope that helps.