Help With Grow Box Design

Hello everyone.

So I went out and purchased my:

Hood
http://www.horticulturesource.com/product_info.php?products_id=658

lights (400w HPS & MH)

and ballast (lumatek 400w)
http://www.growlightexpress.com/grow-light-ballasts-3/400-watt-ballasts-12/lumatek-400-watt-ballast-120-240v-31.html

This grow will be 2 plants at a time using DWC. I am going to build a 3x3x6 growbox, Growing NY Power Diesel and White Rhino. If anyone has any comments on the size of the box please let me know.

I was going to buy a grow tent but I couldn't find one in the size I want. It seems like any tent that is 6 feet is usually made for several plants. So I will be building my own box.

As this is my first box, I have several questions.

First, regarding the hood, does it need a fan on both ends or just one end?

Also, does the cooling of the light take care of the temp, or will I need more fans? What other holes will need to go into it?

I'm also wondering if using a 240v plug is better than using a 120v. I have a 240v plug available if it will help. Another thing regarding the whole electrical; my house is pretty new (2005) and the plugs are right on the opposite side of the wall that houses the breaker. I'm wondering if any special precautions come to mind for the more experienced growers when they look at this setup in this type of house.

One more thing, this may sound weird but I have no idea where the ballast should go. I've checked out many videos and pics of grows but can't ever see it. Any help there is appreciated.;

Thanks

it only requires one fan, you could just connect some air ducting to the other end and make a hole on the wall or ceiling of your grow box, to exhaust the hot air, as for the ballast, place it outside of your grow box on the wall, on the ground, but make sure it's on something fire-proof and heat resistant, as it gets kind of hot, and make sure it doesn't come in contact with children or pets! (last one was common sense, haha)
if you got any more questions, just holla at me!

SLB