That looks like a sweet build, but your PSU is way overpowered. As in you won't reach its sweet spot even running a power virus load and heavy overclocks on both cpu and GPU. A heavily OC'd RX 480 is 200-220W. The 1800X is a 95W TDP chip, and if AMDs demos are accurate pulls 140+W under heavy loads (Cinebench, wasn't it?). With your choice of cooler, I take it you're not planning to OC it to kingdom come. And even with that, and a single ssd + hdd, you might be close to 500W while running some unrealistic power virus, but nowhere near exceeding that. My (currently dead) rig with a heavily overclocked 95W CPU and a Fury X (a 275W GPU) pulled just over 500W from the wall (i.e. including conversion losses, so around 450W actual component power draw) during OCCT+FurMark loads.
Sure, if you go Crossfire down the line you'll exceed 500W easy. But if I were you, I'd get an EVGA G3 750 or 850W. These are arguably the best Gold-rated PSUs out there (check JohnnyGuru), and of much more suitable capacities for your build. And, of course, plenty powerful for Crossfire if the time comes for that.