Start them off with medium intensity lighting. Either one of your led units or the 600w hps mounted a decent distance from the canopy. I don't use the dimmer function on my ballasts, because I believe running a light at less Watts than it is intended will decrease the life of the bulb. This is just my opinion so don't quote me on that. I do have a 1000w ballast that I can run at 40%, 60%, or 100% this means that I can run or 400w bulb at 40%, a 600w bulb at 60% and a 1000w bulb at 100% It also has a 110% function which I do not use, but I dont feel like getting into that right now. Anyway later on in flowering I would recommend using the 600w HPS if you can keep the temperature under control, although this may be over kill for a space 2x4 foot.
As far as getting the most weight in your growing area I would recommend any method to utilize what little horazontal growth you can. Then flip to 12/12 letting the plants continue to grow vertically as they flower. (That is very little space so the sooner you flip the better)
Make the most of the space you have and if putting them outside will work for you and your not worried about all the the factors included in growing outside, do that. Assuming you live in the correct climate for growing and your light cycle will produce the results you wish to obtain.
The height of your finished plants is dependent on the amount of time they are in a vegetative state and the amount of topping or training you do to them. Any plant can finish at 3 feet.
I hoped this information was useful to you as it took me forever to write and I went completely overboard. The best of luck to you.
