Mixing stimulants is a bad idea. Abusing medications that haven't been prescribed for you is a bad idea. Using Hydroxycut by itself (even without the interaction of amphetamines) is a bad idea. So, no.
Yes you should be fine. The Percocet wears off fairly quickly, but it depends on what you mean by "safe". Will you overdose or die? No. Will you feel messed up? Maybe, but it really shouldn't be a problem.
Yes it is safe. I have been taking percocet and excedrin maximum strength for years, but as always its safer to consult your doctor for reassurance due to the face that nobody knows your current medical history. I say yes.