PSU - Seasonic M12II 620 watts will do. The money you save can be re-allocated to other components.
RAM - Make it 8GBx2. In case you need more RAM in the future, add another set of 8GBx2 for a total of 32GB.
GPU - Get the 8GB variant of Radeon RX 480
Monitor - Why not consider the LG 34UC97 which was reviewed by Linus ?