I'll try to answer to all the questions together
Damaged to the CPU can occur when to much voltage is applied and the CPU is not cooled properly, so if you keep the CPU properly cooled then you don't have to worry to much about voltages as long as you don't go crazy (keep voltages bellow 1.5V) and look out for the temperatures (don't go over 75ºC when in stress testing)
If you run into stability issues just dial back the overclock