You probably should be worried about the thermocouple if you have never done it before. The first issue is which type do you plan to use? What chip do you plane to use? Does that chip have the linearizion routines? What is the temperature range of where your box sits?
In general most people totally ignore the mechanics of connecting the thermocouple and a lot of commercial stuff gets it wrong. You need to make sure that the place you connect the thermocouple doesn't change temperature. It's not just a screw terminal and a sensor nearby, I had some commercial stuff really screw up when there were air currents.
You need two sorts of functions if you decide to do it yourself. One is temperature to voltage, referenced to 0 deg. C) for the temperature range your after and another function that is the inverse of that and returns the mV value of the isothermal block temperature for the range of ambient temperatures expected. referenced to 0C.
You also need to consider open thermocouple detection which is basically an high value pull-up or pull-down. With heaters, you want to read the maximum so the controller shuts off. Maxim and Linear Technology have some nice TC IC's.
"Servo" can mean lots of things and it might require PID.
For seven segment stuff, there are two major types called common-cathode and common-anode. Make sure the display matches the driver. Then the sub-type is multiplexed and non-multiplexed. Again, be careful.
Also watch the 5 V to 3.3 interfacing and vice versa.
Much can be done with chips that use the SPI and I2C busses, including handing interrupts for the switches.