Ryzen 5 soon and RX 500 series same(few weeks) it will be Vega month or whatever longer to wait.
seasonic one you linked are "ok" for a standard pick, but also very old these days so likely overpaying for bronze certified especially considering what is delivered(going back to even 2010 they didnt stand out from the pack performance wise though built well) I have choice for myself of what possibly getting when/if I upgrade, and yes Corsair although good far from best often overpriced cause of branding.
EVGA G2 650w
ThermalTake Toughpower 650W GOLD Modular
Seasonic XP2
IMO any high quality 550-680w range shoot for 40+ amp on 12v to be safe obviously depending on other parts may/may not be using, so can have some wiggle room.
https://linustechtips.com/main/topic/406160-psu-ranking-and-tiers/
I would think about going one step above for 8gb version of RX 480 if choosing to go that route as they use higher speed on memory for them, tend to also be better overclockers as well, do not know for the RX 500 series how they will fare but they supposed to be faster and less expensive even for a "rebrand"
Case wise, that is really a up to user wise, myself was going to go for Fractal Design Define C seems to have what others are offering in a less pricey package lots of little nice things, BUT you more or less have to have modular power supply.
Anyways, good luck on build