first, if you are already using 200w for lighting a 250 wouldnt make a diff in the cost but would be alot better, and a 400w would be twice the cost to run the lights. my 150w and fan only made a difference of about 5$ a month. so if you figure the numbers out it would only make about 10$ difference than what you are paying. other people say around 50w per sq ft to grow plants but i have read that it can be as low as 30w per sq ft and still get good solid budding. i did mine right in the middle, 40w's, thats why i asked the size of your space. if your 400 does get too hot all i can say is good ventilation and air movement. your closet should hold your 4 plants and the 400 light easily enough. otherwise use your spare room, sorry im not being more help it just seems that you can do it in a closet of that size without to much trouble. especially if you are going to get a fan and carbon filter, exhaust it into your spare room instead of letting it run inside of the closet.