Yeah I wouldn't get that light you posted OP, especially if you really want 300w of light in that space. The description tells you that it only runs at 110w max and most of that is creating heat, not light.
Now I'm sure it would grow a plant and produce something that would do the job, but it won't allow your plants to reach their full potential, regardless of how perfect everything else is.
Oh and that "3 year warranty", good luck with that. I'd bet that if something happens after 1 yr they will say either it was something not covered or you did something that voided the warranty, and thats if they even respond or are around any more.
DIY, is the best way to go and with mechatronix passive heatsinks, you can build a light with some wire cutters and a screw driver as the only tools needed. I plan on growing in the same dimensions as you, 2x2, and I got 6 Vero 18s, 4 3k and 2 4k and will run them at 1.05amps.
