spend more on the 1200w psu. a 1000w is pushing it for 6 580s and that's even undervolted. the hx1200 or hx1200i are great choices from corsair.

there are many good gaming boards which support 6 gpus and you can dual use them for gaming, the only issue in your case is the 580 is a weak gaming card. i guess you could stay at 1080p

you can get 6gpu rig racks on amazon for 59 or so. it's easier than building your own

make sure you check that whatever board you get really can support 6 gpus. not all can. 6*150w = 900w + 65w system or 130w or so if you dual mine on the cpu means you have a 1030w draw or about 960w if you don't use the cpu to mine

that's max load on a 1200w psu and too much for a 1000

on a 1200w psu you want to see no more than 1000w on your kill a watt at the wall when you test