Be ez with the Mg man it can give you problems when you start adding nutes to it there are time released ferts in Mg and can confuse shit for a new grower you would be better off buying a bail of sunshine or pro mix somthing more neutral so when you do add nutes you will have a buffer and you...
there are so many variables my man a 600 watt light really wont give u a big enough footprint to cover a 4x4 space with optimal light i use a 1k for a 4x4 area and sometimes i almost hit 2 pounds on a light strain and condition dependent. The trick is be happy with what u get if u pump yourself...
There are a lot of variables man hydro,soil,coco,rockwool? Also your room conditions is it dry humid or just right is it hot or cold ? people wont answer questions like this brotha u need to be more specific but a good rule of thumb is let the plant tell u when it wants water the key to building...