Getting supplies together! Need some advice

I have been doing lots of research for my upcoming first grow. I have most of what I want to do figured out, but was wondering about the compatibility of some of the items I will be getting.

here is what I plan to use so far. I already have a seedling/cloning area setup so this is primarily for veg when plants are strong enough to withstand MH and HPS for flowering.

4'X4'X7' Cabinet/tent
400w hps/mh switchable light/ballast
6" cooltube reflector
6" inline fan rated at 250cfm (light cooling only)
6' inline fan rated at 424 cfm for air exchange (going to use a carbon scrubber. Needs to be = or > cfm rating of fan???)
a fan or 2 for circulation within the grow area
The grow box will be placed in a room that is air conditioned and sits between 72 degrees and 76 degrees depending on my comfort level.

The main reason for my confusion is my fan cfm ratings. I was wonder if I was going overkill or maybe even underkill on it? I have used many of the calculators out there, but have come up with a broad range of results with minor design changes. I plan to keep 90 degree angles to a minimum, but probably will not be able to avoid at least 1 or 2. I was also wondering if I decided to use 1 fan instead of 2 to both cool and scrub what cfm rating would I need to be looking into? If i were to do this it would be something like:

(filter)>(light/hood)>(Inline fan)>(Exhaust port) <add ducting where needed> with the fan pulling air through the filter and light.

I am in the process of rounding up materials and just want to make sure i don't buy an xbox with ps3 controllers!

Hope to see you folks in the grow log section soon

 

Good to know and thanks for the input. I have decided to run with the 2 fan setup.

One final question is would these be sufficient enough if i chose to upgrade to a 600w somewhere down the line? I would hate having to get a whole new vent system just for a future light upgrade.