If you are using the star dawg auto from fastbuds it is listed as a large and tall variety. From the little experience I have, i would say 3 plants in 5 gallon pots for that space. You will need to use low stress training, possibly topping, to control the height. 600 watts for 1.2 sq meters is a lot and will produce lots of heat so you don't want the buds getting to close. Check out my grow of tangerine dream to see the results of 3 large autos in the same size tent in a mix of fox farm ocean forest and happy frog with top dressing to feed. And I only had a 250 watt metal halide. I cant recommend enough, if you are investing in all this gear, to do your research. Check out the website grow weed easy dot com. Almost everything you ever needed to know will be there. Checkout " migro " on youtube which will teach you a lot about indoor lighting. Pod casts I would recommend are " periodic effects", they have some great science of cannabis episodes, also "growcast" and "kis organics". So many excellent resources out there. Dig in brother.