i run a virtually identical set-up, so i've got some feedback for you:
-run an inlet air line to your light from one of the vent holes on the tent. the way you have it set up in your photos, you are using all that nice warm, moist air from inside your tent to cool your light. this causes two problems - the moisture can corrode the electrical connections, and your plants need the humidity especially when they are seedlings. If you live in a dry environment, you might also consider putting in a humidifier. i personally keep the RH at about 60% for the first couple growth stages, and the air temp close to 80 degrees. having the inlet line i described above will keep everything nice and humid without you having to top up the humidifier every day. as well, you may find the carbon filter unnecessary since you won`t constantly be venting the tent air into your house.
-get some micro-nutrients. two part solutions are nice because they're super easy, and they generally work. but you will definitely see increased yields with a broader nutrient spectrum. i use GH products and follow the expert feeding schedule here
http://generalhydroponics.com/site/gh/docs/feeding_sched/GH-FloraSeries-REC-Charts.pdf
-as for the lighting issue, 1000w for 4 plants in the space you have is plenty. I personally use 400w in a 5`x2.7`x6.6` tent and regularly get nearly a pound per plant from three plants
hope this helps. happy growing.