First off; Nice build, you've obviously done some research or taken some good advice on it.
Take your time over the monitor selection, it's the single most important part of the system from a usability point of view, a good one will make using the system a pleasure, a bad one will give you eyestrain and headaches at the very least.
For an all new, startup build I wouldn't recommend a standard 60Hz monitor, gameplay-particularly in fast paced games-is so much smoother and more responsive on a Gsync or Freesync display.
Monitors come in different flavours: TN is fast but their colours aren't always super, they also suffer from 'colour shift' where the colours change if you view the display off centre. This is far less of a problem than in the past and my own TN panel is more than good enough for gaming and movie viewing. IPS and PLS displays are a little slower but have better colour reproduction and don't suffer from the colour shift of TN displays. I'm not aware of any Freesync or Gsync MVA, PVA or VA panels but they are the slowest of the bunch and have the best colour reproduction.
Fast Freesync displays attract a significant price premium over their stock 60Hz companions, and Gsync displays are more expensive still, both will effectively lock you to either AMD (freesync) or Nvidia (Gsync).
Now I'll just throw a few spanners into the works.
With recent price cuts the R9 Nano is only <>£30 more than the R9 390X and it's a better card at 1440 rez, despite 'only' having 4Gb of onboard memory.
Try as I might, I can't justify the big price hike of the GTX980Ti over the R9 Nano, especially when you factor in the higher cost of a compatible Gsync display to partner the Nvidia card.
I'd go for a R9 Nano and a IPS 1440 display to match it-just be VERY careful when selecting the display-Freesync is an open standard so not all monitors support a wide range of operation, you should look for one that spans at least 48-144HZ, check the specs carefully.