looking good bro. as for elements i cant say where to get them but this calculator will help you size them for the oven
http://www.heatershop.com/btu_calculator.htm
at 400 degree rise in temp 7000watts of elements should be enough and that should give you a 32 amp draw. most oven elements i have seen come in the 2000-3000 watt range so 3 2500 watts would be 7500, more than enough. that would be a 35 amp draw and you can run that on a 40 amp circuit for a almost 20 percent safety factor. hope this helps. best of luck bro.