Well, if your gonna grow in a closet and heat is an issue for ya, Id go with either an envirolight (125 or 200w, its up to you) or a few CFL's - highest wattage you can get. Im not sure what wattage CFL's come in, as I prefer the power of a HPS as heat isnt that big of an issue for me. A 400w HPS doesnt produce that much heat anyway, as long as the light is a couple of feet above the plants.
Are you gonna have the plants in different stages of growth, or are you gonna germinate them all at the same time? If youre going to germ them at the same time, a single 200w envirolight would be enough for 4 plants (I think), but you might want to add a few CFL's in at the sides for flowering so the buds get maximum light.
It all depends on your budget really - you can pick up a 600w HPS with ballast and reflector (reconditioned, but lamp is new) for £65 inc. p+p on eBay, which is a pretty good deal. If you have another £100 to spare, you can pick up a decent fan and all the tubing etc for some ventilation. Mylar goes for £2.50 1m x 1.4m, so its pretty cheap considering it reflects something like 98% of the light, and if your growing in a closet toud only need to spend a maximum of a tenner on it. Although it does reflect heat aswell, so in a closet lined with mylar Id go for the envirolights/CFL's, unless you want to generate some more heat in there.
Something I dont have and really need is a thermometer, I should really buy one but Fiona seems to be doing fine, and the temp just above her can be described as 'warm' - around 24C, falling to probably 18-20 at night.