Well it's pretty obvious that ArcGIS Pro will be the new defacto desktop envvironment soon. As for the current ArcGIS desktop, I always leave 64-bit processing off. It usually alleviates about 95% of any potential problems. If I need background processing (which is rare), there is other software outside of the ESRI framework that will allow for that or I'll use a workstation at work precisely for this purpose... set it and leave it.
I use 10.4.1 and dont have serious error
to eliminate error, disable background proc, since this 64bit function pretty much useless
if you want 64bit, go straight to arcgis pro
when you run processing. avoid minimize the program
arcgis 10.5 relatively new. no support yet from most extension.