Four 24" bulbs per shelf sounds right, but, I advise you to initially buy only two 2 bulb fixtures and experimentally compare the results of one versus two fixtures per shelf before investing money in another two fixtures. You should paint the interior of your closet white or line the line the walls, ceiling, inside of the door and shelves with aluminized mylar sheet.

What do you plan to do about ventilation? If the door is closed, which is preferable, you will need forced ventilation to prevent an accumulation of heat. If I were you, I would saw one hole near the top of the door and one hole near the bottom and install two cooling fans, one blowing out at the top and one blowing in at the bottom, connected to a thermostat, set at 80 deg. F., inside the closet.