1.) Yes. You could probably bring down the voltage a little more.
2.) The general rule of thumb is stay under 65C for full load, which is the small FFT test.
3.)The temps from Coretemps are accurate. They reflect your "core temps".
4.) That's entirely up to you. There won't be any notable difference if the timings are set accordingly.
5.) Minimize vcore.
6.) Get your temps lower than 65C and make sure your system passes Prime95's small FFT test for at least 12hours and blend test for at least 14hours. This is because running 24/7 requires longer stressing.
Wow, you sign off quick! As in, if the voltages are on auto, believe it or not, the boards tend to add more voltage than you need, especially to the processor as you up the FSB and therefor the processors speed.
You can look and see where its set at currently while on Auto. (Hopefully your MoBo supports this and shows you the current values as well, even when on auto.)
If you can see it there, just lower it by 2 notches and test away with small ftts on all the cores for a few hours, no BSOD, lower it again by one and re test until you find the lowest stable voltage. That holds true no matter what your speed, because the lowest voltage makes you get the lowest core temps.
Best to do it at night or when you leave for a while, as you want several hours to be sure its stable, then lower, when you reach a point that it fails, up it a notch and let it run all night, 8 hours if possible, and if it bombs out... up it one more and do it again!