OK lets break this down:
[Thermaltake Versa N23 Mid-Tower Chassis with 600W 80+ PSU]
I Chose this case and PSU because its 80+ rated so its a good PSU, and there's nothing worse than getting a new computer, and it looks like crap.
Yeah looks dont matter in performance, but being proud of your new 'toy' is a huge part people dont consider.
[Kingston 16GB kit (2 x 8GB) HX424C15FB2K2/16 Hyper X DDR4 2400Mhz]
This is the fastest RAM a Ryzen board without an updated BIOS will support.
This will be fixed with a BIOS update, but who cares? The extra money you spend on 'faster ram' is unlikely to ever make a user noticeable difference.
[Acer G237HL 23"IPS-LED,16:9,1920x1080,4ms,1000:1,1xVGA,1xHDMI,Speakers,Tilt]
23" is a decent size, and IPS means super bright and colorful, it also means you can view it from almost any angle. IPS is normally limited to 60hz, and will sometimes overclock to 70hz, so if he's COMPETITIVE gaming, even casually, he might want to go to a cheaper TN panel, because they're 'faster', but IPS is new and beautiful. For most people 60hz (60FPS) is enough.
[CM Storm Devastator II Gaming Keyboard & Mouse Red LED]
This combo looks wicked for a cheap keyboard and mouse. Once again, it's about being proud of your new build.
[Seagate ST2000DX002 FireCuda 2TB SATA3 8GB NAND Desktop SSHD]
These, I love. I use them, well their older brother, in every clients build I do. They're a normal 2TB HDD, with X ammount (8GB in this case) of 'SSD' built on.
In the 'old days' this was crap, because you had to run software to use it, and it worked on a file level.
NOW? It runs on BLOCK LEVEL and it's all automatic.
Basically, if you read "Sector 1~250" most often, which is say, PART of your firefox cache file, it'll move those blocks to the SSD so it's instant to load. If the cache file is 10GB and you only read 1GB of it, it'll only clone the 1GB of raw sectors. They're fucking legendary.
Note: If he's not savvy, so he won't do backups, consider a second one, and set up a clone\mirror task so they backup to each other.
[Asus PRIME X370-PRO]
I don't use Gigabyte, too many problems, so this is the cheapest ASUS board that's AM4 and an X370 chipset :)
[AMD Ryzen 5 1500X 4-Core Socket AM4 3.6GHz CPU Processor with Wraith Spire Cooler ]
New RIZEN processor, 4 core, 8 thread.
The reason RIZEN is a good choice (besides bang for buck) is because you can go to an 8 core 16 thread on the SAME SOCKET in the future, when prices drop.
That's future proofing for ya!
See? That's without a Windows Licence, and without a Graphics Card.
For those, I'd suggest:
Windows 10 (cheap from ebay, $25? dodgy? That's up to you....)
a Geforce GTX 1060 (6GB edition) (around the $325 mark).
You need the 6GB edition, because some games are disabling graphics features below 4GB of ram, and the cheaper is 3GB
Hopefully DASA sticks his thread in to tear the shit out of my build, he usually does, though he usually doesn't correct TOO much... but that's what i've got so far.
There really is nowhere to cut, and still be happy, to fit a $300 GPU in there.
$1500 is a realistic budget for 'all brand new',