I agree that thermocouples sound like the best sensors.
Take a look at some of the delta-sigma converters. In one recent design I was able to read thermocouples without any amplification. That's useful since the input offset voltage of a amp can be significant compared to a thermocouple's output voltage. I did add a FET to each input to effectively short it together so that the software could do auto-zero. You will also need a regular temperature sensor on the board because thermocouples only give you relative temperature, not absolute. You need absolute on your board to compute the absolute temperature in the oven. This may sound more complicated than it is.
I would be careful about casting things in concrete. Metal has a way of deteriorating, particularly at high temperature. I think it would be a good idea to allow for replacing the thermocouples and their leads. Maybe you can cast a small conduit in concrete instead of the wires directly. That way you can change the wires thru the conduit while the conduit (just a small pipe) stays in place.
As for getting the data back to the house, it would be useful to know how far that really is. Since this is a one-off and apparently all on your own property, I wouldn't get too worried about your local RF regulations. You can use a fixed directional antenna at both the oven and the house to get longer distance. WiFi sucks a lot of power and will give you much higher data rate than you need, although it would be convenient to connect to on the house side. The oven can be a TCP server that the computer in the house checks in with.
802.15 radios sound more appropriate, although again we need to know the distance. As I said before, two directional antennas would greatly increase distance and chance of anyone else noticing your signal. The Microchip MiWi protocol sounds like it would be a good choice for this. The data rate is low, but that's fine for this application. The nice part is that it's low power and you can shut down the oven side completely between transmissions, with the house side always on because it has much more power available. The drawback is that you then need a MiWi to ethernet bridge, but that's not all that hard.
We're actually working on distributed MiWi modules with a wall-powered base station that reports the collected data over ethernet via a custom TCP server. We've got things mostly working, but haven't released the code or the units yet. The code will be available for free when we do.