Of course that is assuming you are speaking of a Linux VPS, but you didn't mention your OS, so if you are using another one such as Windows they also have benchmark tools available.
There isn't a good number for all those parameters, other than as high as possible for your particular testing subject machine. Just load up as many concurrent connections you can with Jmeter (toying with the balance of instances and threads), and fire to your machine. Do so until a certain component (ie MySQL) fails, then try to optimize that component and fire again.
Best Answer
You can run a stress test on a VPS just as you would on any other system. This could involve:
Of course that is assuming you are speaking of a Linux VPS, but you didn't mention your OS, so if you are using another one such as Windows they also have benchmark tools available.