Ok here are your choices. The elements in the link are 3100 watts so:
3100w X 3 elements = 9300w/240v= 38.75amps
3100w X 4 elements = 12400w/240v= 51.6amps
Using 2400w elements
2400w X 3 elements = 7200w/240= 30amps
2400w X 4 elements = 9600w/240= 40amps
From the above senairos you have two good choices
3100w X 4 elements = 12400w/240v= 51.6amps
Use two of the 40amp contactors as discussed earlier and order 4 matching elements.
2400w X 3 elements = 7200w/240= 30amps
Use one of the 40amp contactors and get 3 matching elements.
You should also be looking at a vent hole and a fan for even heat circulation.
If you decide to go with the two contactor design let me know and I will take some time later tonight to modify the schematic for the additional contactor (you will use the same 220v service). This will probably be the design I use when I build my oven. The switches and temp controler/ thermostat could be used from a donor oven.
This is a great site for info. Thanks to Caswell for providing it for us.
Jason
www.autocyclepc.com