Is it this one? https://www.newegg.com/Product/Product.aspx?Item=N82E16883101344
Looks like it have some Lite-On powersupply those are pretty common on prebuilt OEM PC's.
So you have only one usable ram slot? In that case maybe you should get an AIO first and then upgrade the ram. 8gb is not enough for a system like yours.
Maybe it's not the best one if you want to play only DX8 games and nothing newer. In that case probably some GeForce 6000 series card would be better, anything older than that would be AGP only.
But the thing with 4K UHD is just to get more pixels per inch, so if you have a 24" FHD TV (or monitor) with a good IPS panel it doesn't look worse than a big 4K UHD IPS TV.
That kinda sounds like you think FHD is a low resolution? 24-26" FHD TV have more pixels per inch than your big 4K UHD TV.
Of course it's a lot better experience to watch movies etc. on a big FHD or UHD TV than on a lot smaller TV.
Usually smaller TV's are cheaper ones and only have TN panels.
Maybe you could get some old dual socket LGA1366 server? And then upgrade CPU's to 6 core 12 thread Xeon X5670 or higher.
DDR3 Registered ECC server memory is also really cheap so it should be pretty easy to get 48gb for it.
What about Huawei Honor 9 (64gb)? I've had one for a bit over one year.
CPU on it is almost as powerful as on the Honor 10, GPU is a little bit worse but you said you don't use phone for gaming.
I've heard can overclock it a bit with SetFSB, but I've never tried it myself. I have a Xeon X5677 @ stock (X5690 but with only 4c/8t) on my 6-dimm HP Z400.