No, you cannot use it as a tabletop model as built-In microwave should be built into a cabinet as the sides are exposed without any paneling. Therefore, the exposed sides of the microwave will be very hot when used. The same applies to tabletop model as it cannot be used as a built-In model.
No need to preheat the microwave if you are just using it for reheating purposes. You only need to preheat the microwave if you are doing convection cooking.
When the appropriate temperature has been reached, the beep will sound twice and the temperature set will flash on the electronic LED screen to remind you to place the food into the microwave.
The convection oven cooking is different from microwave cooking because of the different heating functions available in the oven:
(i) Convection function which transfers heat via the hot air circulation assisted by a fan.
(ii) Heating functions via the heating element i.e. top heater, bottom heater and grill.
Microwave oven heats food by passing microwave radiation through it and this wave make the food cooked from within the outer surface and the cooking time is shorter as compared to the oven cooking method.
The proper utensils which can be used for microwave cooking are those that have a statement printed "microwave safe" at the base of the utensils. This means these utensils are certified and safe for use in microwave cooking. Utensils without "microwave safe" should be checked to ensure they are suitable. Place the utensils in the microwave along with a glass filled up with half full of water. Heat up with maximum power or "High" setting for one minute. If the item is hot, you should not use it. If it is just slightly warm, you can use it for reheating but not for cooking purpose.
If the item is maintained at room temperature, it is suitable for microwave cooking. Metal utensils and utensils with metallic trim should not be used in the microwave, unless specifically recommended for microwave use.