The 12 volt rating is the critical thing here. Your PSU is advertised as having 36 amps on the 12 volt rails. Figure 10 amps for an OC'd CPU. Your GPU needs about 9 amps. The motherboard, no more than 2 amps. The two drives, no more than 3 amps. That's 24 amps - max = 288 watts.
Digital logic - no more than 5 amps @ 5 volts, including the drives. Memory - less than 10 amps @ 3.3 volts.Total here, less than 55 watts.
I figure that you can add 20 fans and still not load the PSU to 80% capacity.
Voltage is a measure of the force pushing current (electrons) through a wire. Current is a measure of the amount of electrons being pushed. Think water pressure pushing gallons of water (well, technically "rate of flow") through a hose. Watts is like the total amount of water.
Watts = voltage X current. First estimate - 24 amps X 12 volts = 288 watts.