I wouldn't go with a K series or the accompanying Z series motherboard. If you're not interested in OCing there is no point in paying the extra money. And if you are interested then a small case like the Node will present a very low thermal barrier which limits any potential OCing.
Anyways going off your start I'd do this instead. You could drop down to an i5 if you wanted to, i7 adds very little to nothing to games and no difference between the two in regards to playing 4k video. You'd be cutting it very close with the prebuilt PSU, you can buy the case without one though and supply your own. A 600w should be more than enough to cover a 1070 or 1080 in the future.
One side note I hate those WD NAS units. I think their cheap garbage. I really recommend spending the extra money and getting a least a two bay NAS unit from Qnap or Synology instead. Good luck.\
[PCPartPicker part list](http://pcpartpicker.com/p/pKXMf7) / [Price breakdown by merchant](http://pcpartpicker.com/p/pKXMf7/by_merchant/)
Type|Item|Price
:----|:----|:----
**CPU** | [Intel Core i7-6700 3.4GHz Quad-Core Processor](http://pcpartpicker.com/part/intel-cpu-bx80662i76700) | $297.99 @ B&H
**CPU Cooler** | [CRYORIG C7 40.5 CFM CPU Cooler](http://pcpartpicker.com/part/cryorig-cpu-cooler-c7) | $37.49 @ Amazon
**Motherboard** | [Gigabyte GA-H170N-WIFI Mini ITX LGA1151 Motherboard](http://pcpartpicker.com/part/gigabyte-motherboard-gah170nwifi) | $113.89 @ Amazon
**Memory** | [G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-2400 Memory](http://pcpartpicker.com/part/gskill-memory-f42400c15d16gvr) | $62.99 @ Newegg
**Storage** | [Samsung 850 EVO-Series 500GB 2.5" Solid State Drive](http://pcpartpicker.com/part/samsung-internal-hard-drive-mz75e500bam) | $147.99 @ NCIX US
**Case** | [Fractal Design Node 202 HTPC Case](http://pcpartpicker.com/part/fractal-design-case-fdcanode202bk) | $79.99 @ Amazon
**Power Supply** | [Silverstone 600W 80+ Gold Certified Fully-Modular SFX Power Supply](http://pcpartpicker.com/part/silverstone-power-supply-sstsx600g) | $116.99 @ SuperBiiz
| *Prices include shipping, taxes, rebates, and discounts* |
| **Total** | **$857.33**
| Generated by [PCPartPicker](http://pcpartpicker.com) 2016-05-11 12:17 EDT-0400 |