Can you advise the model of microwave, as each will have its own specification, please also clarify if you mean the maximum heat which should be emitted from the unit (eg the outer case, or the maximum temperature inside the microwave).
Further to our phone call this afternoon, I can confirm that the Microwave oven should not exceed 200 degrees Celsius.
Exceeding this will cause damage to the oven housing and result in excess heat not being able to escape, resulting in the unit overheating as you have noticed in the door getting hot.
The basic principle of a microwave oven is to heat through dielecgtric means via radiation, and not through convection or conduction, so the ambient temperature should not be hot, unless the halogen grill function is on.
It is entirely possible the broken glass turntable could have been through the result of being exposed to a rapid change in temperature, combined with the vibrations from the motor rotating it.
I would not recommend you use this product, as its showing signs of a fault where by the unit is overheating, and poses a significant fire risk.