Heat rocks can burn iguanas and should not be used. Sometimes people wrap heat rocks in towels and other material. This is asking for a fire.
One iguana cage with heat light, UVB light, humidifier and heater is enough for one wall socket. Wall recepticles are usually rated for 15 amperes or 20 amperes. Many extension cords are rated for 13 amperes or less, which means they will fry before they report an overload to the circuit breaker. Do not use an extension cord that you would use for Christmas tree lights to connect the iguana cage. Even if you do not use an extension cord, this does not mean you can plug your radio, TV and computer into the same wall socket as the iguana cage. Try not to overload the recepticle.
Iguanas are famous for knocking over ceramic heaters and light hoods. You may use a screw-in ceramic or porcelin socket base for the heater and lights. If this is not possible, find a way to use the hoods so that the iguana cannot knock the lights over.