i5 4570 = 84 watts
rx 470 4gb = 160W peak
motherboard and drives= 120W
364W with everything working at full.
my estimates are broad and at those numbers are only when running at full throttle. most of the time you will be using under 150W, gaming will increase that to near max but only while gaming or otherwise stressing the system.
450W should be enough if its a good quality 450W unit. not all are made the same what model we talking about here?