In android i can create an emulator with
android create avd
AFAIK you can only use the simulators provided by Xcode - but that should really be all you need. There are fewer variations in hardware in iOS than Android, so there shouldn't be any settings or properties to apply.
As far as running the Simulator app as much as you want, you can certainly do that. The simulator is an app on your computer just like anything else.
Mine is located here (I also believe this is the default path):
I added my simulator app to my dock so I can launch it anytime (also helps with debugging website layout for mobile devices)
Hope this helps.
EDIT: If you need to open from the command line:
will do it