Yo can run your video card fine on that power supply, but you will never reach its best quality. Im running the 4850, they are damn good cards, my stays around 49-53 celcius when i play games i run fan at 75% so it wont heat up.
Damn thats a huge box, when we had puppys last feb we had ours in 4' x 4' and we still have it, cause we kept 2 puppys. Now they sleep in it at night and when we go out. I had boxers so just as big lol.
4 12s would be louder, because more cone area and more heat displacement for the woofers. Also running 4 12s at there max wrms should be fine since they are rated at that, what woofers do you have in mind?
The lvl 4 is rated at 1000wrms, can be push 1500wrms daily if its a clean signal. 2000wrms is more of the lvl4xl range, unless you have a lvl 4 with lvl 5 soft parts. For amps i would pick the audioque, price and clip light.