If you wish to have upgradeable rig later, go for cheapest i3 and r9 270X if your budget allows that. Your PSU should be a quality model of at least 450W, but 550 is preferred for longevity sake and future upgrades. I am not talking cheapo PSUs here, but quality brands like Seasonic, XFX, Corsair (AX, HX, RM series), Antec and so on.