1.If you want to play games in such resolution at max/very high settings you need R9 Fury as minimum. Or wait for RX 490
At high/medium settings RX 480 should be enough.
2.R7 370 doesn't support FreeSync
It all depends on the graphic quality tht you want to play and the game itself.....for minecraft you should be fine but for a game like Deus X mankind evolved maxed out @1440p even an GTX1080 wont make 60fps