Most of your questions are already answered in the guide. For testing 90-95C. For normal operation best hit 80-90C at most. Running 100C for only a little bit won't hurt it, but I don't advise going to sleep for 8 hours while the CPU chugs 100C.
Uncore voltage ups temps but the effect is not that much, as Cygnus noted. Your #1 heater is still your Vcore for sure. Nobody really does SA/Io tweaks for the sake of temperature control, but rather as a last ditch attempt to make the CPU stable at a given speed. The offset range for those three voltages are low, once you step out it may be dangerous. So in terms of temps, I doubt it'll be anything worth noting.
Thanks! Sorry for asking duplicate questions. I'll double-check the guide before I post more.