Since you're using a desktop, what's wrong with the 2018 Mac Mini? Upgradable RAM, storage and GPU can be added externally. Dual 4k support out of the box or a single 5k should be enough for your single monitor?
I know because I tried to do this with a 2018 Mac Mini. Aside from the very lackluster GPU performance, it's a pretty speedy machine.
I had a fairly generous budget for a new computer. 32GB of RAM was about $200 from Crucial. The external SSD storage options were pretty crappy. Any sort of TB3 option was a few hundred dollars to start. I ended up settling with a USB3 2TB HDD. I then had to copy my Photo and iTunes libraries over to it and re-point the apps to the right spots.
For the external GPU, you're looking at about $500 at a minimum. And then you have to find a place for that to sit, and it's essentially the size of a small ITX PC case.
I ended up returning the Mini and just breaking down and building a vanilla hackintosh. A 8700K/32GB/1TB SSD/RX 580 ITX box with quality parts that's all in one small case (Fractal Design Define Nano S) in the same desk footprint as just the external GPU enclosure, and it's not a thermally-constrained dongletown.
Would I recommend it to anyone? No. But after an initially scary couple of hours, I have for all intents and purposes a normally-functioning macOS box that is noticeably quicker than the Mini for the cost of just the base Mini -- sans all the other junk I had to buy. The macOS install is vanilla, with SIP enabled, and no janky kexts in the OS install - NOTHING custom in the OS install. The bare minimum shoved in the EFI partition.
Everything works (sleep, audio, iMessage, etc). It was marginally more trouble than getting Windows 10 installed. Less trouble than getting Ubuntu installed.
God, it's glorious.
As of today, the prices are higher than what I paid. If you're going to buy, monitor /r/buildapcsales on Reddit and buy your parts when they go on sale. I bought my stuff over a period of a couple weeks and saved substantial money.
Samsung SSD prices fluctuate by 10s of dollars. Other SSD manufacturers such as Intel and WD offer steep discounts at times. The RX 580 GPUs go on significant sales pretty often.
At some point, I need to finish my guide and publish to Github. I largely followed corpnewt's Vanilla Guide for Mojave [1], and followed the Coffee Lake train. It's important to follow each step closely.
Again, I do not recommend a hackintosh, but for me it worked out really well.
1. https://hackintosh.gitbook.io/-r-hackintosh-vanilla-desktop-...
I don't really get the resistance about adding some external cables/cases to your desk. The desk has always been full of cables anyways (monitors, speakers, consoles, even my mechanical keyboard etc.) and I don't see any harm in adding a couple more for an external SSD and an eGPU. As mentioned by some other commentators, I'm pretty much past the days of having to constantly fight my main setup and just want to have everything working flawlessly most of the time.
I plan to get a Mac Mini soon and try it out. I think the performance should suffice for most of my use cases. If it seriously stutters I'll consider building a Hackintosh, or simply do those demanding tasks on another dedicated box.
This would be my choice over a hackintosh for parents or other family.
Sounds like something that could be 3D printed or
One big plus: it's quiet, so I can leave it on.