Jam is right, I have the same deal, I have a 1000W cabinet and a smaller one for moms and clones with 175MH and 6 23w CFL's.
Never the less, if you want to do it your way we are here to help. Pros and cons of flowering on top or bottom. Usually your flowering plants will be heavier do to bigger plants and pots, so some rather have them on the bottom so not to have a collapsing shelf, or so not to lift them down all the time for watering. With the fan there all ready it will be a little easier to keep that light cooler, but even when people split the cab they still place the fan up top even when the top is used for veg. If the veg was on top then you would place some3 IN, or 2 1/2 inch holes in that shelf and place black PVC pipes going down into the bottom compartment with 90 degree elbows facing the back of the cab or to the right and left, then you could place black pantyhose on the ends of the pvc piping, on each end. This combined with the blackness of the pipe that makes it more difficult to reflect light and with the elbow that makes a turn, killing more traveling light will give you the air flow between sections without light problems. Now remember this all sounds fine in theory, but when you do it, it can be a pane. Also you have to separate the sections for when you open the door, because you may want to check on clones or other veging plants and want to open the door, but the flowering plants are in their dark cycle so you have to separate the flowering section with something like Panda film and use a peal and stick zipper and hot glue the Panda film all around the edges.
Well any questions just ask.
Adieu