Good questions!

I use 2x250 watts, they work well but I don't know how pinpoint I can answer you since I use them side by side. As far as using it in a 3 x 3 area, you shouldn't have too many problems depending on how many you're planning on growing.. I would also recommend to throw a few CFLs in there to get the lower growth since the 250 doesn't have as much light penetration through the leaves. But then again, that also depends on how many you're planning on growing, wether you LST, scrog, ect.

Heat wise.. well, I was keeping the temps down really well last night but I'm using a portable swamp cooler x 3 fans.