first grow plz help

This is My first grow. I'm using a home made deep water hydroponic setup. basically a home made version of the stealth hydro bubbleponics system. but with a larger airstone. my grow box will be L-4'XW-4'XH-6' and the inside either painted white or coated with mylar. this box pretty much has to be in my attic unfortunately. which means heat i think will be an issue. right now i have already bought a 150-watt HPS light which they say puts off 18,000 lumens i was also thinking of installing 4 cool spectrum 40-watt CFLs so i can get both light spectrums. i was thinking of growing like 4-6 plants of the auto-flowering Diesel Ryder. My main concern is with light i need to keep the heat down, and im not sure if the light plan that i have will be enough light as it is. im already planning on installing a small exhaust fan to keep heat down and also have inlet holes. any input would help. will this be enough light? is there a better way to cool the box? if i made the box smaller would i need to use less light? any other tips or advice on anything else. im a complete noob so any help would be good.

bump any input appreciated.

I think you should rig everything up and find out what the temp is. It's the only way to find out for sure. Just don't go cracking any beans before you get all this sorted out. As for the amount of light, I think 4 plants would be good, 6 is kinda pushing it I think unless you add more light, but again, you need to establish some kind of baseline before you go adding more lights.