I think that you might be able to go with a 90CFM Dayton fart fan as an active intake and try the 400W depending on the ambient/room temps. For light proofing, on my cab I took thick tarp and made a velcro frame on all 4 corners and got a tarp zipper for the middle so I could have easier access. You can get the tarp zippers at Lowes or Home Depot, they are zippers with an adhesive sticky strip that you stick to the tarp and then cut a line up the tarp to open the zipper up and down with. You can put a zipper on each side so that the whole tarp opens. By the way I have a cab with the same dementions from there, I think it is a Kolman cabinet. I have a 175 MH in it for mothers and clones and an optional 6X23W CFL rack that I can put up when needed. I only have a 230 CFM bathroom for outtake.
PS. Those 90 CFM Dayton fans are only$30 at most hydro stores.
Adieu