If you can get a big enough fan and some cfls in the reddish spectrum for flower you should be fine...Dont know what kind of fluoros are reddish but I am sure some one out here can help you find them.
For vegging I would just use the halide and save the fluoros for flower, or vice versa to save on electricity. If you do use fluoros for veg instead of your 400, than be sure to use the bluish spectrum. (Sry I dont know the name for fluoros but I use HID only) Other wise enjoy..and remember environment makes you or breaks you, so invest in a good ventilation system up front.