go with computer fans - just keep adding them in an in-line fashion (entry and exit) until you get the right temp. inside the box. humidity should fall to a reasonable level if your air exchange is good enough. Heat rises, so the exit fan(s) should be at the top of the box - entry near the bottom.
you'll need about 2000 lumens for the space... but at only 2 feet high, your plants might not do so well as you'll only be vegging them to perhaps 10". Perhaps less given the space taken by potting soil and the bulbs.
