Oh, nice, a Davinci Resolve user. So here's what you'd need -
Monitors - only one game in town here, the LG 27UD68P. Won't get a better 4K monitor in this price range. Pretty accurate at sRGB, which is close enough to Rec.709. Doesn't cover DCI-P3, but then you aren't going to show your films in theaters either. Get a second monitor - it can be cheap. It'll give you a lot of screen real estate.
RAM - You're going to need at least 24 GB for 4K work. 32 GB preferably, of course. 16 GB leads to some slow downs when the clips thumbnails are loading from RAW etc.; or when there are intense effects.
CPU - Multi-threaded is key. Go with a Ryzen 7 1700X since you aren't overclocking.
GPU - Is crucial for Resolve if you're doing some advanced grading. Vega 56 is an absolute monster at Resolve, but I guess for your usage something like a RX 580 or GTX 1060 will suffice. Avoid the 3 GB 1060 though.
SSD - If you really want to grade RAW 4K files, you are going to need to run it all of a SSD. You could also look at RAID HDDs, which could be a cheaper option, but may not be as reliable.
ProRes is much easier to deal with, of course.
Lastly, Mac machines are no good for serious 4K colour grading in Davinci Resolve. There simply isn't a machine powerful enough. The iMac Pro will finally change that, but obviously that's a future product way out of your budget. You won't get drivers for the modern GPUs needed for 4K even if you build a Hackintosh. I'd recommend Windows 10 Pro if you want control over your updates etc.