It’s currently 4:50am from where I’m from so I’ll try to get back to you on this after I get some sleep. But at least let me give you some quick input on my part.
(I apologize if I’m rambling in the post or if I’m giving some huge mis-info. Really sleepy, I’m just forcing myself to make the post because reasons)
So for the CPU, I would suggest you aim going for the AMD Ryzen 5 1600 since it’s (arguably) cheaper and (is already proven) to work better than some i5 or i7 6000 or 7000 series. Do not downgrade for the Ryzen 5 1400 since there will be a huge performance difference (check the YT vids, the 1400 is a good entry level CPU Ryzen-wise, but the 1600 is the bang-for-the-buck CPU Ryzen-wise).
For the GPU, I’m assuming from the builds you’ve posted that your minimum us at least 1080p at 60FPS so I would suggest aiming for either a Nvidia GTX 1060 OR an AMD RX 580 since these two cards are proven to be able to provide those numbers. If some fo you are wondering why I’m not suggesting an RX 570, it’s because an RX580 is a few currencies higher than the 570 BUT the added VRAM helps and the 570 is really just a downgrade 5804 GB.
For the HDD, IF a Western Digital Cavier Blue 2TB IS CHEAPER than the one on the build, then get the WD. If not, then go get the Seagate Barracuda that you’ve listed.
For PSU, Seasonic is always a good brand.
For RAM, I would suggest going for 16GB DDR4 via 2 x 8GB DDR4 RAM IF YOU CAN AFFORD IT else just go for an 8GB DDR4 RAM.
Because you are aiming for an ATX build, I’m not going to be able to suggest cases (I’m more of a M-ITX or M-ATX guy).
Sadly, because suggesting you a better mobo than the one you’ve listed will take me an hour or two, I’d rather skip that for now.
Are you sure you want that optical drive (the DVD/CD Writer)? Not a lot of PC builds use some Optical Drives and you can install Windows 10 via a Flash Drive (and removing the Optical Drive will save you a few bucks)
Hope this helps.