For ‘idle’ power draw, a reading was taken after having Windows open on the desktop for 30 minutes. A reading under load was taken with Prime 95’s SmallFFt test running alongside 3DMark Fire Strike.
Total power draw is barely half of the power supply's 600W rating, so adding in a second RX 580 for CrossFire down-the-line would be no problem.
The X370 mobo would have been a good choice if the PSU could handle crossfire. The CPU is also a bit on the edge for crossfire – a 1600 or 1600X would have cut it imo. Then again, those two things would have driven up the price. I have to agree that a B350 mobo would have been the best choice.