I think you've made some great choices, a 1070 is great for 1440p gaming
520W power supply is sufficient, I'd say not much point going above 600W - in this case I would be more concerned about the quality of the PSU since your specs really only use 350-400W load (from what I've read, the evo version seems better if you can get it, although the standard version is still great)
In case you aren't completely sure I am using a 1070, DDR3 ram and a 3rd gen i7 with a 450W mini-itx power supply. No issues at all.