Advice First Build

Solution
Nice build. I do always recommend a 500gb + SSD, depending on how you use it. Reason being, you need enough room for the OS, all games and applications to be installed on the SSD. This will speed everything up. You dont want to fill a SSD completely full because performance will suffer. GTA5 would take 25% of a 250gb SSD (just an example at 65GB)

So if you feel 250 is enough then pull the trigger. :)
Nice build. I do always recommend a 500gb + SSD, depending on how you use it. Reason being, you need enough room for the OS, all games and applications to be installed on the SSD. This will speed everything up. You dont want to fill a SSD completely full because performance will suffer. GTA5 would take 25% of a 250gb SSD (just an example at 65GB)

So if you feel 250 is enough then pull the trigger. :)
 
Solution
Pretty solid. My thoughts are below...

MEM - The Z170 chipset can handle modules faster than DDR4-2400, but do NOT go over 1.2v. The modules below are a good option along with the ones you choose.
SSD - The Sandisk X400 is relatively new and benefits from a low price (at the moment). The 512GB for $130 is really hard to beat. Along with X400 and Samsung EVO, I also like Crucial.
HD - Eh... 2GB is much nicer to have.
PSU - The 650w is a bit much for your needs. Look toward the EVGA 550w G2, Seaconic G 550w or XFX XTR 550w.

Enjoy that build!

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor ($238.99 @ SuperBiiz)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($43.53 @ Amazon)
Motherboard: Gigabyte GA-Z170X-Gaming 5 ATX LGA1151 Motherboard ($134.99 @ Micro Center)
Memory: G.Skill Ripjaws 4 Series 16GB (2 x 8GB) DDR4-2800 Memory ($64.99 @ Newegg)
Storage: Sandisk X400 512GB 2.5" Solid State Drive ($130.99 @ Newegg)
Storage: Western Digital Blue 2TB 3.5" 5400RPM Internal Hard Drive ($69.98 @ OutletPC)
Video Card: EVGA GeForce GTX 1070 8GB SC Gaming ACX 3.0 Video Card ($449.99 @ SuperBiiz)
Case: Phanteks Enthoo Pro M ATX Mid Tower Case ($74.99 @ Amazon)
Power Supply: EVGA SuperNOVA G2 550W 80+ Gold Certified Fully-Modular ATX Power Supply ($70.98 @ Newegg)
Total: $1279.43