I read somewhere that you'll need 750W for a Gigabyte 270X 4GB. My total wattage for my build comes to about 363 watts so could I get away with a CX 500M or? Heres the build http://pcpartpicker.com/p/3yTHK
Yes you can.
Side question. Why an MSI Gaming motherboard if you're going for a non K cpu and 1600 ram?