Your high school wood shop teacher would be proud!
Seriously that's a rockin' cabinet and my only 2 suggestions to increase efficiency are:
-Get that 400 HPS on a light mover or if you haven't bought it yet, look into a pair of 250s side by side instead to take advantage of the long, skinny space.
-Active intake is shooting yourself in the foot if it is not perfectly matched to your active exhaust. Take the smaller active intake fan, and use it as an exhaust for the 'veg' section, which is going to get HOT when you fire up the HPS downstairs. Allow passive intake through a good-sized hole cut low in each chamber. Run the exhaust on your HPS pulling air THROUGH an air-cooled hood and out- the order will be: Open end in grow room-> through light hood -> through ductwork -> through blower -> through carbon filter. Putting the filter after the blower dampens soud significantly. Also, hanging the blowers free, by soft, but heavy, ropes, dampens the vibration and makes them even QUIETER.
You can easily stuff a second shop light up top for happier seedlings.

Looks EXCELLENT so far. Good luck.

EDIT: Oh shit I didn't see the interior setup. But the active intake/active ehxaust suggestion still stands. I'm impressed by your tidy ducting and all.