help with rig building?

hi , so , i started to build a rig.
i have 3 gpus , 1x470 , 1x480 , 1x580 , and yes i will get more.
1 motherboard biostar tb85 + cpu
ram , ssd.
i'm trying to find a psu now. how much would i need for 6 gpu? 1200 , 1500 w?
do i need a cooler for the cpu on the motherboard?
do i need a power on button?
thank you for your help