Did you see the dimensions of his box? There is no way you are going to put in 2 HPS in there. That would require duct work, fans and 2 HPS lights, which would run about $400+.
Your box will not be big enough for your plants. One plant alone will fill that box before you get to flower.
Im a CFL grower. I have found that you are better off with lots of lower wattage lights than fewer higher wattage lights because of heat and light distribution, plus if one light goes, you have more that are still on.
If you go CFL i suggest clamp lights. They can be moved around easily and if you get the kind where you can remove the clamp and reflector, you can use them for hanging lights.
You know about light color temperatures and photoperiods for the stages of the plant right?