First Grow..Closet Grow..Any advice appreciated!!!

Ok this is my first grow. My set up is inside my bedroom closet, which is 2.5 ft x 4 ft floor space and 8ft tall. I have cut an exhaust hole in one the walls for my intake and another hole up high on another oposite wall for exhaust with a vent leading out my window. My walls are painted with flat white paint and every thing is very tight. Well for lights right now i have a 250 watt hps, but it points down,verticall, and i dont like that so i plan on buying a new 400watt hps/metal halide sometime within the first week of my grow. (seeds should arrive tomorow hopefully". Mainly what im wondering is how many plants i could fit in there? is it worth my time and effort to try and split the closet in the middle and use both the lights i'll have? are both my lights in that small area a waste of light? and is there a way to grow plants taller and skinnier without losing bud in the end???...any input would be appreciated. I plan on maybe doing a journal and loading pics..we'll see..thanks.

a 400watt bulb is perfect for your place.

As far as your plant layout, i would recommend you split the box into 2 vertical boxes. This is good idea for a few reasons:
-to grow your plants 6 feet tall in that narrow of a box could be a problem. You could probably fit 3 plants in there
-If you separated it into 2 boxes, you can use 1 for flower and one for growing so you always have plants flowering. You could possibly fit 6 plants in each box
-you could fit more, smaller plants in your box instead of a few lanky-er ones. small plants are easier to take care of and they generally have more bud sites
-this is especially perfect for you because you can use your 250w for vegging and use your 400 for flowering

Extra tip: Your plants will grow another 12-16 inches when they flower, so make your flowering box that much bigger