I'm struggling with very similar issues. Sometimes it freezes while I'm actively using it. I see a spinning beach ball that doesn't recover. Can't seem to interrupt it, or get any response. Eventually the screen goes black.and then nothing until I restart.
Most often the freeze happens overnight, but at different times. My system is set not to sleep, only turn off the display. If I hit a key on the keyboard the display comes on and I see a mouse cursor on a black screen, but the cursor won't move.
The Console logs never show nothing useful preceding the freeze. I never see any on-screen errors during the freeze. I've got an external PTRG system monitoring SNMP of the Hackintosh. That confirms there is no runaway memory or CPU processes that precede a freeze.
I'm using an NVIDIA 740 with NVIDIA's drivers and two 27" displays. As an experiment I removed the NVIDIA card and ran on integrated Intel graphics for a while. I still had the freezing, though it seemed less frequent.
I've also tried with and without my iCloud account logged in.
The only odd-ball thing I'm doing is a custom "Fusion" drive which combined a M.2 SSD with a 2TB SATA drive. Everything else is very typical.
The freezing is more irritating than anything else. Hitting the reset button gets me back in business in about 30 seconds. I'd love to solve it though, and appreciate any advice.