by "interfaces" I was referring to circuitry; I'm not up to speed on how to connect a controller to switches, relays, thermistors, etc.
That will depend on the specific relays, switches, thermistors, etc.
Switches are pretty simple. Connect one side to ground. Connect the other side to a digital pin. Set the pin to INPUT, and enable the pullup resistor. Use digitalRead() to see if the switch is pressed (the value will be LOW) or released (the value will be HIGH).
Relays generally draw more current than the Arduino can provide, so a transistor is needed. Wiring the transistor to the relay, the power supply, and the Arduino is pretty straight-forward. I even managed to do it.
A thermistor typically has just two wires. One side connects to +V. The other side connects to an analog pin.
As for the programming, I volunteered in reply #1 to help. PM me, if you want.