what to look for in a HPS bulb..

:question: so what i got for yall is kinda open ended..
first off i have a 600w ballast.. for HPS lights. one hell of a heat problem. and a smell one too. (goal of stealth grow when i am done)
so i am thinking about redesigning the grow environment..
what i have to know is
first: can i run MORE than one bulb off one ballast? even if both bulbs are under the total wattage?
second: what do i want to look for in a bulb? (i am gonna supplement with a pair of 42w 6500k CFLs for blue spec light) such as color temp and size thoughts.. i am thinking about a 250w or maybe 2x 150w or something like that..
third: what kind of heat can i expect in an ~ 2 ft x 3 ft area ~ 4 ft tall..
fourth: anything else yall can think of that i need to know..

You can only run one bulb off of one ballast unless you buy one of the special ballasts that will take multiple bulbs.
As far as the difference in bulbs, Its a crapshoot. I've bought both expensive and cheap hps 1000w bulbs and the only difference I've found is most of the time the cheaper bulbs last longer.
Hard to tell if you're going to have heat problems till you do it. Just build the room with ventilation in mind so that if it needs the extra ventilation you'll be able to do it.