While I'm no expert, for vegging I do 24/0 or 18/6. For flowering I do 12/12 and nothing else. Your size desires will depend on the strain. Do you know if it's indica or sativa or some hybrid? From my experience with sativas, they shoot for the stars after you switch the light cycle to flower them. Indica does the same thing but not to the degree of a sativa. If you're wanting 4 to 6 stalks up to three feet tall, you might need some more light.