So, your main usage will be gaming...
What aspect ratio monitor are you wanting? 16:9 (current "standard" widescreen)? 21:9 (emerging "ultra-wide")?
What size monitor? 23"? 27"? Bigger?
What refresh rate would you want for your selection of games? 60Hz? Faster?
What is your likely budget? (planning on buying new or used?)
PS: Have you checked compatibility between i5-4690K and MSI Z87 MPOWER board? (Should it not be a Z97 chipset for a 4690K?)
Putting in a 1000w PSU for potential future SLI when one GPU is a GTX980ti means buying another GTX980ti at some future date - that's the big-ticket item in your current rig - sounds like a massive overkill (not the PSU but 2 x GTX980ti)... Are you planning on a multi-monitor setup?
In the short-term - i.e. while you have a single GPU - I'd suggest a 16:9 1440p gaming monitor with a highish refresh rate (120Hz or better), then when (and if) you get your SLI in place, get a second monitor of the same spec. In that way, you can upgrade GPU capacity and screen real-estate in synch. Going for a 4K monitor on a single GPU (even a GTX980ti) will restrict your frame rate initially PLUS you will pay a fair premium for a 4K monitor over a 1440p screen, making any future screen expansion rather costly.
It's all about balance...
I hope that helps...
Dave