A slightly different take.
You can use the SSD as a disk. If you do, delete the 2nd SSD from my build.
You might or might not be able to re-use the license. Is your OS associated with your Microsoft account? Is it an OEM license or a retail one? Is it the free one? (as in you upgraded from Windows 7 or 8) then it is different still. I'll link a the bottom how to do that.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel - Core i5-8600K 3.6GHz 6-Core Processor ($279.89 @ B&H)
CPU Cooler: Noctua - NH-D15S 82.5 CFM CPU Cooler ($78.99 @ Newegg)
Motherboard: ASRock - Z370 Pro4 ATX LGA1151 Motherboard ($129.99 @ SuperBiiz)
Memory: G.Skill - Ripjaws V Series 16GB (2 x 8GB) DDR4-3000 Memory ($149.99 @ Newegg)
Storage: Samsung - 850 EVO 250GB M.2-2280 Solid State Drive ($104.00 @ Newegg Marketplace)
Storage: Western Digital - Caviar Green 2TB 3.5" 5400RPM Internal Hard Drive ($59.09 @ Newegg Marketplace)
Video Card: MSI - GeForce GTX 1080 8GB DUKE OC Video Card ($514.98 @ Newegg)
Case: Fractal Design - Define R5 (Black) ATX Mid Tower Case ($79.99 @ Newegg)
Power Supply: SeaSonic - FOCUS Plus Gold 650W 80+ Gold Certified Fully-Modular ATX Power Supply ($83.99 @ SuperBiiz)
Total: $1480.91
This build has a faster CPU, better cooler (I don't trust those AIO), faster ram, faster disk, better video card, better power supply.
I like Vapours build more than sr71-blackbirds. Mine is similar to his. I did it slightly differently.
For openers I think 3 disks is the right way to go. 1 m.2 or SSD for fast booting and ideally long life. Re-installing the OS can be a time consuming task for many.
The second SSD is for apps and games. This disk is designed to be used, abused and then die.
The third disk is a larger HD. This is for backups.
Copy everything from D: to E:\backups\d
when D dies, replace it and copy everything back. Also backup work in progress (images, videos, word files, etc) even games.... want to try a new stupid mod, copy the game folder over.
The only area where I feel Vapours build is better is he went with the 8700k and in order to keep in about the same pricing as the other builds was to trim the CPU slightly. But read the below link and see if it matters to you. The 8700k adds approximately $120 to the build, and omitting it let me include a 1080 and stay under the other prices without compromising quality.
For this build I assumed you would use your current SSD as the APP disk (the disk which is to be killed by over use), and the faster m.2 for a boot disk and so used a lower power (and lower heat) HD for backups. No need spending the extra for a BLACK disk for backups when a GREEN one will do the job just as well.
review on the 8600k
http://www.tomshardware.com/reviews/intel-coffee-lake-core-i5-8600k-cpu,5264.html
how to move the free license
https://www.howtogeek.com/226510/how-to-use-your-free-windows-10-license-after-changing-your-pc%E2%80%99s-hardware/
Since we're all picking your PSU choice, here is some info you will likely find helpful:
https://linustechtips.com/main/topic/631048-psu-tier-list-updated/