Ya i really dont want to sell anybody anything, lol hell i will need it again . the 400 watt HPS from HTGsupply is 150 Shipped on ebay still an awesome deal, but temps get hotter with that 400 watter.
And to answer your question about the different wattages. if you buy a 150 watt hps ballast hood, and bulb, you cannot upgrade with a bigger bulb you would need a 400 watt ballast and bulb,ect. So if you want to upgrade just get the 400 watter off the bat, but it is more expensive to run as frar as ur light bill goes, my light bill went from 32 bucks a month to 85 so ya you do the math, and that was only 12/12 i used my150 watter for veg so 18/6 lightss then i could not imagine 18/6 or even 24/7 with a 400 watter shit getz expensice.