Power Supply Amperage Help! (6 replies)

I am designing a printer and I have purchased a RAMPS kit and four stepper motors.
Each stepper motors is 1.5 Amps
I will also need a heated bed plate (plugged into D8)
(This is all going to run at 12V by the way)

Now for my questions: Can my heated bed plate be more than 11A if I buy a power supply capable of giving that much power? Is anything else using power from that half of the power terminal?

For the other half of the power terminal, I guess that I will need at least 6 Amps for the stepper motors plus some power for the Arduino and fans etc. or am I overcomplicating things because I will theoretically never have all four motors at full speed at once?

Also, how do I know how much power goes into each half of the terminal when purchasing a power supply? I found: http://www.makergeeks.com/5012siatxpos.html which has a nice tutorial on how to install it. It shows this on the bottom of the page. Can someone help with interpretation?

DC Output Specifications:
+3.3V, 22A
+5V, 30A
+12V, 22A
-12V, 0.8A
+5VSB, 3A

Thanks a ton in advance!
~Evan