I have built about 35 years ago a 8 cuft. kiln with a turntable in the floor. It is heated by a single Silicon Carbide element and max input is about 15 kW. It fires to cone 10 . The advantage of the turntable is the heating is very uniform because tyhe heat transfer is mostly radiation and the rotation ensures uniformity, and a single element works fine. The turntable also makes loading easy . I would be happy to share details. The insulation is fiber plus 2600board. Efficiency is high so cost to fire is low. The controller I built allows for 16 discreet power levels but I would like to change to the Raspberry Pi controller so I dont have to watch it so often.