Make sure that the controller can operate a solid state relay (ssr), these can also be purchased on ebay. Choose a ssr that matches you kilns current draw and voltage requirement (if your kiln is 3 phase you will need three ssrs). A controller that does not have a ssr output can be used with the controllers internal mechanical relays but then you will need an extra power supply to power a mechanical relay for the kiln.
The controller should be a pid controller so it will automagicaly adjust itself to your kiln. If you buy a controller with ramp and soak you can then fuse and slump glass which is nice if you make architectural lighting. In fact I think that glass and iron work well together. If you get a controller with ramp/soak features you can also do controlled anneals. I like Honeywell and Omron controllers.
Get a type "K" thermocouple they are made in different lengths to reach the interior of you kiln, you should also get a ceramic sleeve to protect the thermocouple. I get my thermocouples from a ceramic/pottery supply but they are also available on ebay.
If you choose to use a Honeywell or Omron contoller use there web sites to help decode the product feature codes that are on the controllers.
One last thing get a fan or small blower to keep your ssr cool.
I hope this helps a little.
brad