The MOBO itself needs 35~55W.
Obviously, adding components requires more power. Further, you need to be very careful calculating the correct PSU size. Meaning if the calculated use is e.g. 550W then you need to add a minimum of 30% to allow for electrolytic capacitor aging and even more if you plan to OC either or both the CPU & GPU(s).
As above if the requirement is 550W X 1.30 = 715W so look at 750W.
I recommend Corsair PSU {Japanese capacitors, Single rail, voltage protection} http://www.corsair.com/learn_n_explore/ {Power Supply Finder tab}