I use a MacPro from 2009 and it works OK in most instances.
Much of the setup in Resolve is ‘virtual’ in that you can work on camera
RAW files that don’t have to be EXR to be functional. EXRs are a good way
to save the files and export to facilities because it can capture everything
that was done (if you are careful).
Similar tricks can be used that were done a decade ago for 2K workflows: use a
proxy format for work in progress so that the machine responds speedily, and only put out the high
resolution version for export.
Best hardware specs is in the eye of the beholder, and I suspect it may not get answered here. The data bandwidth requirements uncompressed are about 50% higher with 16-bit per pixel. EXR has some lossless compression modes that can be used in the format if you need to save on disk space, but then
playback can suffer. B44 in EXR was designed for realtime 4K playback but is slightly lossy.
When exporting to EXR, remember that the viewing LUT needs to be turned off in the render so that only the grade is baked in. (i.e. no ODT)
Hope this is a start.