If it'd save you some money, CFLs are perfect for vegging and for seedlings, and would eliminate the need for the MH bulb or a switchable ballast. Not sure if that's an air-cooled reflector or not, but that's something to consider if not, or a cooltube (which is what I like, nice and space-efficient). Also, digital ballasts are nice: quiet and generate far less heat.

Don't neglect ventilation. In fact, for a closet, I'd make sure I have the ventilation stuff figured out before doing anything else, including buying lights. Great lights and piss poor ventilation = dead plants. Heh.