Hell yeah, nice work man!! Rep++
I agree with motherlode, circulation is probably your biggest concern right now. Lighting=A+, Dimensions=A- (not gonna get any monsters in there...make sure not to veg for too long or you will be cursing the height of your box).
In my opinion, your passive intake is too small, there is some formula to create the best air flow, and I think you are supposed to make your intake at least the same area as your outtake (pi*5"^2). Not sure what your temps will be in the area you are gonna be growing in, but having good air flow makes it MUCH easier to control the temps inside your box. Fans inside the box can help like motherlode suggested.
If a lot of air gets through that black plastic cover you have on the front, you can pretty much ignore what I wrote above, because that could suffice as intake.
What strains you putting in there? Keep us posted man, can't wait to see this baby in action. After one more grow in my rubbermaid, I am planning on making something very similar to this, probably out of an old dresser. You definitely did your research, and seriously look into those Ona buckets before you drop $130 or w/e on a carbon filter. You can make your own carbon filters for wayyy cheaper than that!
EDIT:
Checked my facts. A general rule of thumb for passive intake is twice the area of your exhaust. Or...1 sq foot of intake for every 580 CFM (check ur fan). So basically make two holes each the size of your fan if you chose to follow my advice!
