I build incubators out of old freezers and refrigerators. They're well insulated and have tons of wiring to work with already built into them. I have the design and construction notes on my web site (see below).
The features you're talking about are usually part of the thermostat control. In the Helix proportional thermostats they incorporate a dialer module that connects to the thermostat and to an available phone line. If, the temperature of the room the incubator is in rises above the internal temperature of the incubator or the thermostat somehow malfunctions, the thermostat can have no effect on lowering the temperature of the incubator, in these cases the dial up feature is invaluable.
Another feature you might consider adding is some kind of automatic venting feature. Even if the temperature of the room around the incubator does not rise above the internal temperature of the incubator, fluctuations in temperature can lead to higher temperature than you would like. Giving the warm air somewhere to go, allows the internal temp of the incubator to stay more steady. So adding a vent that automatically opens and closes as temperatures reach certain levels would be a great feature.
Just some thoughts.
Regards.

Raintree Herpetoculture